{"id":624561,"date":"2023-09-01T11:56:53","date_gmt":"2023-09-01T11:56:53","guid":{"rendered":"https:\/\/www.indcareer.com\/schools\/?p=624561"},"modified":"2023-09-01T11:57:14","modified_gmt":"2023-09-01T11:57:14","slug":"kc-sinha-exercise-11-1-mathematics-solution-class-10-chapter-11-circles","status":"publish","type":"post","link":"https:\/\/www.indcareer.com\/schools\/kc-sinha-exercise-11-1-mathematics-solution-class-10-chapter-11-circles\/","title":{"rendered":"KC Sinha: Exercise 11.1 &#8211; Mathematics Solution Class 10 Chapter 11 Circles"},"content":{"rendered":"\n\n\n\n\n<h4 class=\"wp-block-heading\" id=\"h-question-1\">Question 1<\/h4>\n\n\n\n<p><strong>The length of a tangent from a point A at a distance 5cm from the centre of a circle is 4cm. Find the radius of the circle.<\/strong><\/p>\n\n\n\n<p>Sol :<br>Let the centre of circle be O so that AO = 5 cm<br>Tangent is AB whose length is 4 cm<br>OB is radius as shown<br><img loading=\"lazy\" decoding=\"async\" height=\"122\" src=\"https:\/\/www.indcareer.com\/schools\/wp-content\/uploads\/2023\/09\/1545814005126169.jpg\" width=\"191\"><br>Now we know that radius is perpendicular to point of contact<br>Hence OB is perpendicular to AB<br>Hence&nbsp;\u2220ABO = 90\u00b0<br>Consider \u0394ABO<br>Using Pythagoras theorem<br>\u21d2&nbsp;AB<sup>2<\/sup>&nbsp;+ OB<sup>2<\/sup>&nbsp;= AO<sup>2<\/sup><br>\u21d2&nbsp;4<sup>2<\/sup>&nbsp;+ OB<sup>2<\/sup>&nbsp;= 5<sup>2<\/sup><br>\u21d2&nbsp;16 + OB<sup>2<\/sup>&nbsp;= 25<br>\u21d2&nbsp;OB<sup>2<\/sup>&nbsp;= 25 \u2013 16<br>\u21d2&nbsp;OB<sup>2<\/sup>&nbsp;= 9<br>\u21d2&nbsp;OB = \u00b13<br>As length cannot be negative<br>\u21d2&nbsp;OB = 3 cm<br>Hence length of radius is 3 cm<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h4 class=\"wp-block-heading\" id=\"h-question-2\">Question 2<\/h4>\n\n\n\n<p><strong>Rajesh is 29 m away from the centre of a circular flower bed. Find the distance he has to cover to reach the flower bed along the tangential path if the radius of the flower bed is 20m.<\/strong><\/p>\n\n\n\n<p>Sol :<br>Let the centre of circular flower bed be O and radius OB = 20 m<br>Let Rajesh is at point A, and he has to travel tangential path to reach flower bed which is AB as shown<br><img loading=\"lazy\" decoding=\"async\" height=\"165\" src=\"https:\/\/www.indcareer.com\/schools\/wp-content\/uploads\/2023\/09\/154581400588565.jpg\" width=\"275\"><br>Now we know that radius is perpendicular to point of contact<br>Hence OB is perpendicular to AB<br>Hence&nbsp;\u2220ABO = 90\u00b0<br>Consider \u0394ABO<br>Using Pythagoras theorem<br>\u21d2&nbsp;AB<sup>2<\/sup>&nbsp;+ OB<sup>2<\/sup>&nbsp;= AO<sup>2<\/sup><br>\u21d2&nbsp;AB<sup>2<\/sup>&nbsp;+ 20<sup>2<\/sup>&nbsp;= 29<sup>2<\/sup><br>\u21d2&nbsp;AB<sup>2<\/sup>&nbsp;= 29<sup>2<\/sup>&nbsp;&#8211; 20<sup>2<\/sup><br>Using a<sup>2<\/sup>&nbsp;\u2013 b<sup>2<\/sup>&nbsp;= (a + b)(a \u2013 b)<br>\u21d2&nbsp;AB<sup>2<\/sup>&nbsp;= (29 \u2013 20)(29 + 20)<br>\u21d2&nbsp;AB<sup>2<\/sup>&nbsp;= 9 \u00d7 49<br>\u21d2&nbsp;AB = \u221a(9 \u00d7 49)<br>\u21d2&nbsp;AB = \u00b1 (3 \u00d7 7)<br>\u21d2&nbsp;AB = \u00b121<br>As length cannot be negative<br>\u21d2&nbsp;AB = 21 m<br>Hence Rajesh has to cover 21 m to reach the flower bed along the tangential path.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h4 class=\"wp-block-heading\" id=\"h-question-3\">Question 3<\/h4>\n\n\n\n<p><strong>Find the length of the tangent drawn from a point, whose distance from the centre of a circle is 5c, and the radius of the circle is 3 cm.<\/strong><\/p>\n\n\n\n<p>Sol :<br>Let A be the point at distance of 5 cm from the centre as AO = 5 cm<br>AB is the tangent at point B as shown<br>OB is the radius which is 3 cm<br><img loading=\"lazy\" decoding=\"async\" height=\"177\" src=\"https:\/\/www.indcareer.com\/schools\/wp-content\/uploads\/2023\/09\/1545814006651347.jpg\" width=\"278\"><br>Now we know that radius is perpendicular to point of contact<br>Hence OB is perpendicular to AB<br>Hence&nbsp;\u2220ABO = 90\u00b0<br>Consider \u0394ABO<br>Using Pythagoras theorem<br>\u21d2&nbsp;AB<sup>2<\/sup>&nbsp;+ OB<sup>2<\/sup>&nbsp;= AO<sup>2<\/sup><br>\u21d2&nbsp;AB<sup>2<\/sup>&nbsp;+ 3<sup>2<\/sup>&nbsp;= 5<sup>2<\/sup><br>\u21d2&nbsp;AB<sup>2<\/sup>&nbsp;+ 9 = 25<br>\u21d2&nbsp;AB<sup>2<\/sup>&nbsp;= 25 \u2013 9<br>\u21d2&nbsp;AB<sup>2<\/sup>&nbsp;= 16<br>\u21d2&nbsp;AB = \u00b14<br>As length cannot be negative<br>\u21d2&nbsp;AB = 4 cm<br>Hence length of tangent is 4 cm<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h4 class=\"wp-block-heading\" id=\"h-question-4\">Question 4<\/h4>\n\n\n\n<p><strong>A point P is 13 cm from the centre of the circle. The length of the tangent drawn from P to the circle is 12cm. Find the radius of the circle.<\/strong><\/p>\n\n\n\n<p>Sol :<br>Let the centre of circle be O so that PO = 13 cm<br>Tangent is PB whose length is 12 cm<br>OB is radius as shown<br><img loading=\"lazy\" decoding=\"async\" height=\"144\" src=\"https:\/\/www.indcareer.com\/schools\/wp-content\/uploads\/2023\/09\/1545814007422316.jpg\" width=\"232\"><br>Now we know that radius is perpendicular to point of contact<br>Hence OB is perpendicular to PB<br>Hence&nbsp;\u2220PBO = 90\u00b0<br>Consider \u0394PBO<br>Using Pythagoras theorem<br>\u21d2&nbsp;PB<sup>2<\/sup>&nbsp;+ OB<sup>2<\/sup>&nbsp;= PO<sup>2<\/sup><br>\u21d2&nbsp;12<sup>2<\/sup>&nbsp;+ OB<sup>2<\/sup>&nbsp;= 13<sup>2<\/sup><br>\u21d2&nbsp;OB<sup>2<\/sup>&nbsp;= 13<sup>2<\/sup>&nbsp;&#8211; 12<sup>2<\/sup><br>\u21d2&nbsp;OB<sup>2<\/sup>&nbsp;= 169 \u2013 144<br>\u21d2&nbsp;OB<sup>2<\/sup>&nbsp;= 25<br>\u21d2&nbsp;OB = \u00b15<br>As length cannot be negative<br>\u21d2&nbsp;OB = 5 cm<br>Hence length of radius is 5 cm<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h4 class=\"wp-block-heading\" id=\"h-question-5\">Question 5<\/h4>\n\n\n\n<p><strong>If d<sub>1<\/sub>, d<sub>2<\/sub>&nbsp;(d<sub>2<\/sub>&lt;d<sub>1<\/sub>) are the diameters of two concentric circles and chord of one circle of length C is tangent to other circle, then prove that d<sub>2<\/sub><sup>2<\/sup>&nbsp;= C<sup>2<\/sup>&nbsp;+ d<sub>1<\/sub><sup>2<\/sup>.<\/strong><\/p>\n\n\n\n<p>Sol :<br>Let the two concentric circles have the centre O and let AB be the chord of an outer circle whose length is D and which is also tangent to the inner circle at point D as shown<br><img loading=\"lazy\" decoding=\"async\" height=\"225\" src=\"https:\/\/www.indcareer.com\/schools\/wp-content\/uploads\/2023\/09\/154581400819270.jpg\" width=\"226\"><br>The diameters are given as d<sub>1<\/sub>&nbsp;and d<sub>2<\/sub>&nbsp;hence the radius will be d12 and d22<br>In \u0394OAB<br>\u21d2&nbsp;OA = OB \u2026radius of the outer circle<br>Hence \u0394OAB is an isosceles triangle<br>As radius is perpendicular to tangent OC is perpendicular to AB<br>OC is altitude from the apex, and in an isosceles triangle, the altitude is also the median<\/p>\n\n\n\n<p>Hence&nbsp;&nbsp;AD=DB=C2<br>Consider \u0394ODB<br>\u21d2&nbsp;\u2220ODB = 90\u00b0 \u2026radius perpendicular to tangent<br>Using Pythagoras theorem<br>\u21d2&nbsp;OD<sup>2<\/sup>&nbsp;+ BD<sup>2<\/sup>&nbsp;= OB<sup>2<\/sup><br>\u21d2d2222+C222=d2122<br>Multiply the whole by 2<sup>2<\/sup><br>\u21d2&nbsp;d<sub>2<\/sub><sup>2<\/sup>&nbsp;+ C<sup>2<\/sup>&nbsp;= d<sub>1<\/sub><sup>2<\/sup><br>Hence proved<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h4 class=\"wp-block-heading\" id=\"h-question-6\">Question 6<\/h4>\n\n\n\n<p><strong>Prove that the line segment joining the point of contact of two parallel tangents to a circle is a diameter of the circle.<\/strong><\/p>\n\n\n\n<p>Sol :<br><img loading=\"lazy\" decoding=\"async\" height=\"179\" src=\"https:\/\/www.indcareer.com\/schools\/wp-content\/uploads\/2023\/09\/1545814011965824.jpg\" width=\"185\"><br>Let lines AP and BR are parallel tangents to circle having centre O<br>We have to prove that AB is the diameter<br>To&nbsp;prove AB as diameter, we have to prove that AB passes through O which means that points A, O and B are on the same line or collinear<br>OA is perpendicular to PA at A because the line from the centre is perpendicular to the tangent at the point of contact<br>PA || RB<br>Hence OA is also perpendicular to RB<br>\u21d2&nbsp;OA perpendicular to PA and RB \u2026(i)<br>Similarly, OB is perpendicular to RB at B because the line from the centre is perpendicular to the tangent at the point of contact<br>PA || RB<br>Hence OB is also perpendicular to PA<br>\u21d2&nbsp;OB perpendicular to PA and RB \u2026(ii)<br>From (i) and (ii) we can say that OA and OB can be same line or parallel lines, but we have a common point O which implies that OA and OB are same lines<br>Hence A, O, B lies on the same line, i.e. A, O and B are collinear<br>Thus AB passes through O<br>Hence AB is the diameter<br>Hence, the line segment joining the point of contact of two parallel tangents to a circle is a diameter of the circle.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h4 class=\"wp-block-heading\" id=\"h-question-7\">Question 7<\/h4>\n\n\n\n<p><strong>Prove that the perpendicular at the point of contact of the tangent to a circle passes through the centre.<\/strong><\/p>\n\n\n\n<p>Sol :<br>Let there be a circle with centre O and BR as tangent with the point of contact as B<br><img loading=\"lazy\" decoding=\"async\" height=\"199\" src=\"https:\/\/www.indcareer.com\/schools\/wp-content\/uploads\/2023\/09\/1545814012744563.jpg\" width=\"225\"><br>Let AB be the line perpendicular to BR<br>\u21d2&nbsp;\u2220ABR = 90\u00b0 \u2026(i)<br>As OB is the radius of the circle and we know that radius is perpendicular to the tangent at the point of contact<br>OB is perpendicular to BR<br>\u21d2&nbsp;\u2220OBR = 90\u00b0 \u2026(ii)<br>Equation (i) and (ii) implies that<br>\u21d2&nbsp;\u2220ABR =&nbsp;\u2220OBR<br>This&nbsp;is only possible iff A and O lie on the same line or A and O are the same points<br>Case 1: Suppose A and O are on the same line<br>If A and O are on the same line, then the perpendicular AB to tangent BR has passed through the centre<br>Case 2: suppose A and O are the same points<br>As O itself is the centre of the circle, and A and O are the same points hence the perpendicular to the tangent at the point of contact passes through the circle<br>In any scenario, the line has to pass through the centre.<\/p>\n\n\n\n<p>Hence, the perpendicular at the point of contact of the tangent to a circle passes through the centre<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h4 class=\"wp-block-heading\" id=\"h-question-8\">Question 8<\/h4>\n\n\n\n<p><strong>Two concentric circles are of radii 10 cm, and 6 cm Find the length of the chord of the larger circle which touches the smaller circle.<\/strong><\/p>\n\n\n\n<p>Sol :<br>Let the two concentric circles have the centre O and let AB be the chord of an outer circle whose length is D and which will also be tangent to the inner circle at point D because it is given that the chord touches the inner circle.<br>The radius of inner circle OD = 6 cm and the radius of outer circle OB = 10 cm<br><img loading=\"lazy\" decoding=\"async\" height=\"223\" src=\"https:\/\/www.indcareer.com\/schools\/wp-content\/uploads\/2023\/09\/1545814013485136.jpg\" width=\"227\"><br>In \u0394OAB<br>\u21d2&nbsp;OA = OB \u2026radius of outer circle<br>Hence \u0394OAB is isosceles triangle<br>As radius is perpendicular to tangent OC is perpendicular to AB<br>OC is altitude from apex and in isosceles triangle the altitude is also the median<br>Hence AD = DB<br>Hence AB = 2DB<br>Consider \u0394ODB<br>\u21d2&nbsp;\u2220ODB = 90\u00b0 \u2026radius perpendicular to tangent<br>Using Pythagoras theorem<br>\u21d2&nbsp;OD<sup>2<\/sup>&nbsp;+ BD<sup>2<\/sup>&nbsp;= OB<sup>2<\/sup><br>\u21d2&nbsp;6<sup>2<\/sup>&nbsp;+ BD<sup>2<\/sup>&nbsp;= 10<sup>2<\/sup><br>\u21d2&nbsp;36 + BD<sup>2<\/sup>&nbsp;= 100<br>\u21d2&nbsp;BD<sup>2<\/sup>&nbsp;= 100 \u2013 36<br>\u21d2&nbsp;BD<sup>2<\/sup>&nbsp;= 64<br>\u21d2&nbsp;BD = \u00b18<br>As length cannot be negative<br>\u21d2&nbsp;BD = 8 cm<br>\u21d2&nbsp;AB = 2 \u00d7 8 \u2026since AB = 2BD<br>\u21d2&nbsp;AB = 16 cm<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h4 class=\"wp-block-heading\" id=\"h-question-9\">Question 9<\/h4>\n\n\n\n<p><strong>(i) A circle is inscribed in a \u0394ABC having sides BC, CA and AB 16 cm, 20 cm and 24 cm respectively as shown in the figure Find AD, BE and CF.<\/strong><\/p>\n\n\n\n<p><strong>(ii) If AF=4cm, BE=3cm, AC=11cm, then find BC.<\/strong><br><strong><\/strong><br>Sol :<br>i) Tangents drawn from external point are equal<br>AD and AF are tangents from point A<br>\u21d2&nbsp;AD = AF = a<br>BF and BE are tangents from point B<br>\u21d2&nbsp;BD = BE = b<br>CD and CE are tangents from point C<br>\u21d2&nbsp;CF = CE = c<br><img loading=\"lazy\" decoding=\"async\" height=\"226\" src=\"https:\/\/www.indcareer.com\/schools\/wp-content\/uploads\/2023\/09\/1545814015685552.jpg\" width=\"215\"><br>From figure<br>We have AC = AF + FC<br>\u21d2&nbsp;20 = a + c \u2026(i)<br>Also, AB = AD + DB<br>\u21d2&nbsp;24 = a + b \u2026(ii)<br>And CB = CE + EB<br>\u21d2&nbsp;16 = c + b \u2026(iii)<br>Add (i), (ii) and (iii)<br>\u21d2&nbsp;20 + 24 + 16 = a + c + a + b + c + b<br>\u21d2&nbsp;60 = 2(a + b + c)<br>\u21d2&nbsp;a + b + c = 30 \u2026(iv)<br>Substitute (i) in (iv)<br>\u21d2&nbsp;20 + b = 30<br>\u21d2&nbsp;b = 10<br>Substitute (ii) in (iv)<br>\u21d2&nbsp;24 + c = 30<br>\u21d2&nbsp;c = 6<br>Substitute (iii) in (iv)<br>\u21d2&nbsp;16 + a = 30<br>\u21d2&nbsp;a = 14<br>Hence AD = a = 14 cm, BE = b = 10 cm and CF = c = 6 cm<br>ii)<br><img loading=\"lazy\" decoding=\"async\" height=\"211\" src=\"https:\/\/www.indcareer.com\/schools\/wp-content\/uploads\/2023\/09\/1545814016498319.jpg\" width=\"224\"><br>Tangents drawn from external point are equal<br>CF and CE are tangents from point C<br>\u21d2&nbsp;CF = CE = c<br>From figure<br>AC = AF + FC<br>\u21d2&nbsp;11 = 4 + c<br>\u21d2&nbsp;c = 7 cm<br>Hence EC = c = 7 cm<br>We have BC = BE + EC<br>\u21d2&nbsp;BC = 3 + 7<br>\u21d2&nbsp;BC = 10 cm<br>Hence BC is 10 cm<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<p>Question 10<\/p>\n\n\n\n<p><strong>In the given figure, ABCD is a quadrilateral in which \u2220D=90\u00b0. A circle C (O,r) touches the sides AB, BC, CD and DA at P,Q,R,S respectively, If BC =38 cm, CD=25 cm and BP=27 cm, find the value of r.<\/strong><br><strong><\/strong><\/p>\n\n\n\n<p>Sol :<br>r is the radius which is OR = r<br>Consider quadrilateral DROS<br>\u21d2&nbsp;\u2220RDS = 90\u00b0 \u2026given<br>\u21d2&nbsp;\u2220DRO = 90\u00b0 \u2026radius is perpendicular to the tangent<br>\u21d2&nbsp;DR = DS \u2026tangents drawn from the same point are equal<\/p>\n\n\n\n<p>As the adjacent angles are 90\u00b0 and adjacent sides are same hence DROS is a square<br>Hence OR = DR = r \u2026(i)<br>As tangents drawn from the same point are equal<br>BQ and BP are tangents drawn from B<br>\u21d2&nbsp;BQ = BP<br>\u21d2&nbsp;BQ = 27 cm \u2026BP is 27 cm given<br>From figure<br>\u21d2&nbsp;BC = BQ + QC<br>\u21d2&nbsp;38 = 27 + QC \u2026BC is 38 cm given<br>\u21d2&nbsp;QC = 11 cm<br>CQ and CR are tangents drawn from C<br>\u21d2&nbsp;CQ = CR \u2026tangents from same point<br>\u21d2&nbsp;CR = 11 cm<br>Again from figure<br>\u21d2&nbsp;CD = CR + RD<br>\u21d2&nbsp;25 = 11 + r \u2026CD is 25 given and RD = r from (i)<br>\u21d2&nbsp;r = 14 cm<br>Hence r radius is 14 cm<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h4 class=\"wp-block-heading\" id=\"h-question-11\">Question 11<\/h4>\n\n\n\n<p><strong>In the given figure, O is the centre of two concentric circles of radii 4 cm and 6cm respectively. PA and PB are tangents to the outer and inner circle respectively. If PA=10cm, find the length of PB up to one place of decimal.<\/strong><br><strong><\/strong><\/p>\n\n\n\n<p>Sol :<br>Consider \u0394POA<br>OA = 6 cm \u2026radius of the outer circle<br>PA = 10 cm \u2026given<br>\u2220OAP = 90\u00b0 \u2026radius is perpendicular to the tangent<br>Hence \u0394POA is right-angled triangle<br>Using Pythagoras<br>\u21d2&nbsp;OA<sup>2<\/sup>&nbsp;+ AP<sup>2<\/sup>&nbsp;= OP<sup>2<\/sup><br>\u21d2&nbsp;6<sup>2<\/sup>&nbsp;+ 10<sup>2<\/sup>&nbsp;= OP<sup>2<\/sup><br>\u21d2&nbsp;36 + 100 = OP<sup>2<\/sup><br>\u21d2&nbsp;OP<sup>2<\/sup>&nbsp;= 136 \u2026(i)<br>Consider \u0394PBO<br>OB = 4 cm \u2026radius of inner circle<br>\u2220OBP = 90\u00b0 \u2026radius is perpendicular to the tangent<br>Hence \u0394POB is right-angled triangle<br>Using Pythagoras<br>\u21d2&nbsp;OB<sup>2<\/sup>&nbsp;+ BP<sup>2<\/sup>&nbsp;= OP<sup>2<\/sup><br>Using (i)<br>\u21d2&nbsp;4<sup>2<\/sup>&nbsp;+ BP<sup>2<\/sup>&nbsp;= 136<br>\u21d2&nbsp;16 + BP<sup>2<\/sup>&nbsp;= 136<br>\u21d2&nbsp;BP<sup>2<\/sup>&nbsp;= 120<br>\u21d2&nbsp;BP = 10.9 cm<br>Hence length of PB is 10.9 cm<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h4 class=\"wp-block-heading\" id=\"h-question-12\">Question 12<\/h4>\n\n\n\n<p><strong>Show that the tangents at the extremities of any chord of a circle make equal angles with the chord.<\/strong><\/p>\n\n\n\n<p>Sol :<br><img loading=\"lazy\" decoding=\"async\" height=\"172\" src=\"https:\/\/www.indcareer.com\/schools\/wp-content\/uploads\/2023\/09\/1545814018788681.jpg\" width=\"227\"><br>Let the circle with centre O and chord PQ with tangents from point A as AP and AQ as shown<br>We have to prove that&nbsp;\u2220APQ =&nbsp;\u2220AQP<br>Consider \u0394OPQ<br>\u21d2&nbsp;OP = OQ \u2026radius<br>Hence \u0394OPQ is an isosceles triangle<br>\u21d2&nbsp;\u2220OPQ =&nbsp;\u2220OQP&nbsp;\u2026base angles of isosceles triangle \u2026(a)<br>As radius OP is perpendicular to tangent AP at point of contact P<br>\u21d2&nbsp;\u2220APO = 90\u00b0<br>From figure&nbsp;\u2220APO =&nbsp;\u2220APQ +&nbsp;\u2220OPQ<br>\u21d2&nbsp;90\u00b0 =&nbsp;\u2220APQ +&nbsp;\u2220OPQ<br>\u21d2&nbsp;\u2220APQ = 90\u00b0 &#8211;&nbsp;\u2220OPQ \u2026(i)<br>As radius OQ is perpendicular to tangent AQ at point of contact Q<br>\u21d2&nbsp;\u2220AQO = 90\u00b0<br>From figure&nbsp;\u2220AQO =&nbsp;\u2220APQ +&nbsp;\u2220OPQ<br>\u21d2&nbsp;90\u00b0 =&nbsp;\u2220AQP +&nbsp;\u2220OQP<br>\u21d2&nbsp;\u2220AQP = 90\u00b0 &#8211;&nbsp;\u2220OQP<br>Using (a)<br>\u21d2&nbsp;\u2220AQP = 90\u00b0 &#8211;&nbsp;\u2220OPQ \u2026(ii)<br>Using (i) and (ii), we can say that<br>\u21d2&nbsp;\u2220APQ =&nbsp;\u2220AQP<br>Hence proved<br>Hence,&nbsp;the tangents at the extremities of any chord of a circle make equal angles with the chord<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h4 class=\"wp-block-heading\" id=\"h-question-13\">Question 13<\/h4>\n\n\n\n<p><strong>In the given figure, a circle touches all the four sides of a quadrilateral ABCD whose three sides are AB = 6cm, BC = 7cm, and CD = 4cm. Find AD.<\/strong><br><strong><\/strong><\/p>\n\n\n\n<p>Sol :<br>Mark the touching points as P, Q, R and S as shown<br><img loading=\"lazy\" decoding=\"async\" height=\"231\" src=\"https:\/\/www.indcareer.com\/schools\/wp-content\/uploads\/2023\/09\/1545814020301459.jpg\" width=\"269\"><br>As tangents from a point are of equal length we have<br>AQ = AR = a<br>BR = BS = b<br>CP = CS = c<br>DP = DQ = d<br>From figure<br>\u21d2&nbsp;BC = BS + SC<br>\u21d2&nbsp;7 = b + c<br>\u21d2&nbsp;b = 7 \u2013 c \u2026 BC is 7 cm given \u2026(i)<br>Also,<br>\u21d2&nbsp;DC = DP + PC<br>\u21d2&nbsp;4 = d + c<br>\u21d2&nbsp;c = 4 \u2013 d \u2026 DC is 4 cm given \u2026(ii)<br>And<br>\u21d2&nbsp;AB = AR + RB<br>\u21d2&nbsp;6 = a + b \u2026 AB is 6 cm given<br>\u21d2&nbsp;a = 6 \u2013 b<br>Using (i)<br>\u21d2&nbsp;a = 6 \u2013 (7 \u2013 c)<br>Using (ii)<br>\u21d2&nbsp;a = 6 \u2013 (7 \u2013 (4 \u2013 d))<br>\u21d2&nbsp;a = 6 \u2013 (7 \u2013 4 + d)<br>\u21d2&nbsp;a = 6 \u2013 7 + 4 \u2013 d<br>\u21d2&nbsp;a + d = 3<br>\u21d2&nbsp;AQ + QD = 3 \u2026since AQ = a and QD = d<br>From figure AQ + QD = AD<br>\u21d2&nbsp;AD = 3 cm<br>Hence AD is 3 cm<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h4 class=\"wp-block-heading\" id=\"h-question-14\">Question 14<\/h4>\n\n\n\n<p><strong>(i) From an external point P, tangents PA and PB are drawn to a circle with centre O. If CD is the tangent to the circle at the point E and PA = 14 cm, find the perimeter of&nbsp;PCD.<\/strong><\/p>\n\n\n\n<p><strong>(ii) If PA = 11cm, PD = 7 cm, then DE = ?<\/strong><br><strong><\/strong><br>Sol :<br>i) From P we have tangents PA and PB<br>Hence PA = PB \u2026tangents from same point are equal \u2026(a)<br>Point C is on PA<br>From C we have tangents CA and CE<br>\u21d2&nbsp;CA = CE \u2026tangents from same point are equal \u2026(i)<br>Point D is on PB<br>From D we have two tangents DE and DB<br>\u21d2&nbsp;DE = DB \u2026 tangents from same point are equal \u2026(ii)<br>Consider \u0394PCD<br>\u21d2&nbsp;perimeter of \u0394PCD = PC + CD + PD<br>From figure CD = CE + ED<br>\u21d2&nbsp;perimeter of \u0394PCD = PC + CE + ED + PD<br>Using (i) and (ii)<br>\u21d2&nbsp;perimeter of \u0394PCD = PC + CA + DB + PD<br>From figure we have<br>PC + CA = PA and DB + PD = PB<br>\u21d2&nbsp;perimeter of \u0394PCD = PA + PB<br>Using (a)<br>\u21d2&nbsp;perimeter of \u0394PCD = PA + PA<br>\u21d2&nbsp;perimeter of \u0394PCD = 2(PA)<br>PA is 14 cm given<br>\u21d2&nbsp;perimeter of \u0394PCD = 2 \u00d7 14<br>\u21d2&nbsp;perimeter of \u0394PCD = 28 cm<br>ii) PA = 11 cm \u2026given<br>using (a)<br>PB = 11 cm<br>From figure<br>\u21d2&nbsp;PB = PD + DB<br>Using (ii)<br>\u21d2&nbsp;PB = PD + DE<br>\u21d2&nbsp;11 = 7 + DE \u2026PD is 7 cm given<br>\u21d2&nbsp;DE = 5 cm<br>Hence DE = 5 cm<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h4 class=\"wp-block-heading\" id=\"h-question-15\">Question 15<\/h4>\n\n\n\n<p><strong>In two concentric circles, prove that all chords of the outer circle which touch the inner arc of equal length.<\/strong><\/p>\n\n\n\n<p>Sol :<br>Let O be the centre of concentric circles with radius \u2018r\u2019 and \u2018R\u2019 (R&gt;r) and AB be the chord which touches the inner circle at point D<br>We have to prove that AB has a fixed length<br><img loading=\"lazy\" decoding=\"async\" height=\"229\" src=\"https:\/\/www.indcareer.com\/schools\/wp-content\/uploads\/2023\/09\/1545814022585367.jpg\" width=\"225\"><br>Consider \u0394OAB<br>OA = OB \u2026radius<br>Hence \u0394OAB is an isosceles triangle<br>Radius OD is perpendicular to tangent AB at the point of contact D<br>Hence OD is the altitude, and we know that the altitude from the apex of the isosceles triangle is also the median<br>\u21d2&nbsp;AD = BD \u2026(a)<br>Now consider \u0394ODB<br>\u21d2&nbsp;\u2220ODB = 90\u00b0 \u2026radius is perpendicular to tangent<br>Using Pythagoras<br>\u21d2&nbsp;OD<sup>2<\/sup>&nbsp;+ BD<sup>2<\/sup>&nbsp;= OB<sup>2<\/sup><br>The radius are OB = R and OD = r<br>\u21d2&nbsp;r<sup>2<\/sup>&nbsp;+ BD<sup>2<\/sup>&nbsp;= R<sup>2<\/sup><br>\u21d2&nbsp;BD<sup>2<\/sup>&nbsp;= R<sup>2<\/sup>&nbsp;&#8211; r<sup>2<\/sup><br>\u21d2&nbsp;BD = \u221a(R<sup>2<\/sup>&nbsp;&#8211; r<sup>2<\/sup>) \u2026(i)<br>From figure<br>\u21d2&nbsp;AB = AD + BD<br>Using (a)<br>\u21d2&nbsp;AB = BD + BD<br>\u21d2&nbsp;AB = 2BD<br>Using (i)<br>\u21d2&nbsp;AB = 2\u221a(R<sup>2<\/sup>&nbsp;&#8211; r<sup>2<\/sup>)<br>Here observe that AB only depends on R and r which are fixed radius of inner circle and outer circle.<br>And as the radius of both the circle will not change however one may draw the chord the radius will always be fixed.<br>And hence AB won\u2019t change AB is fixed length<br>Hence proved<br>Hence,&nbsp;in two concentric circles, all chords of the outer circle which touch the inner circle are of equal length.<\/p>\n\n\n\n<div class=\"wp-block-buttons is-layout-flex wp-block-buttons-is-layout-flex\">\n<div class=\"wp-block-button\"><a class=\"wp-block-button__link has-primary-background-color has-background wp-element-button\" href=\"https:\/\/www.indcareer.com\/schools\/kc-sinha-solutions\/\">KC Sinha Solutions<\/a><\/div>\n\n\n\n<div class=\"wp-block-button\"><a class=\"wp-block-button__link has-primary-background-color has-background wp-element-button\" href=\"https:\/\/www.indcareer.com\/schools\/kc-sinha-solution-for-class-10\/\">KC Sinha Class 10 Solutions<\/a><\/div>\n<\/div>\n","protected":false},"excerpt":{"rendered":"<p>Question 1 The length of a tangent from a point A at a distance 5cm from the centre of a circle is 4cm. Find the radius of the circle. Sol :Let the centre of circle be O so that AO = 5 cmTangent is AB whose length is 4 cmOB is radius as shownNow we [&hellip;]<\/p>\n","protected":false},"author":302,"featured_media":624584,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"newspack_featured_image_position":"","newspack_post_subtitle":"","newspack_article_summary_title":"Overview:","newspack_article_summary":"","newspack_hide_updated_date":false,"newspack_show_updated_date":false,"footnotes":""},"categories":[24],"tags":[],"boards":[],"class_list":["post-624561","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-class-10","entry"],"yoast_head":"<!-- This site is optimized with the Yoast SEO Premium plugin v27.0 (Yoast SEO v27.1.1) - https:\/\/yoast.com\/product\/yoast-seo-premium-wordpress\/ -->\n<title>KC Sinha: Exercise 11.1 - Mathematics Solution Class 10 Chapter 11 Circles - IndCareer Schools<\/title>\n<meta name=\"description\" content=\"Question 1 The length of a tangent from a point A at a distance 5cm from the centre of a circle is 4cm. 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