The radii of two concentric circles are 13 cm and 8 cm. AB is a

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 Multiple Choice QuestionsShort Answer Type

261. A circle is touching the side BC of  ΔABC at P and touching AB and AC produced at Q and R respectively. Prove that  

AQ space equals space 1 half space left parenthesis Perimeter space of space increment space ABC right parenthesis
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262. In the given figure, the incircle of ΔABC, touches the sides BC, CA and AB at D, E and F respectively. Show that AF + BD + CE = AE + BF + CD

equals space 1 half left parenthesis perimeter space of space increment space ABC right parenthesis




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 Multiple Choice QuestionsLong Answer Type

263. ABCD is a quadrilateral such that ∠D = 90°. A cirlce C (O, r) touches the sides AB, BC, CD and DA at P, Q, R and S respectively. If BC = 38 cm, CD = 25 cm and BP = 27 cm, Find r.
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 Multiple Choice QuestionsShort Answer Type

264. In figure. XP and XQ are tangents from X to the circle with ccentre O. R is a point on the circle. Prove that XA + AR = XB + BR?
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265. In figure a circle touches the side BC of ΔABC at P and touches AB and AC produced at Q and R respectively. If AQ = 5 cm, find the perimeter of ΔABC.



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 Multiple Choice QuestionsLong Answer Type

266. In the given figure, ABC is a right-angled triangle with AB = 6 cm and AC = 8 cm. A circle with centre O has been inscribed inside the triangle. Calculate the value of r, the radius of the inscribed circle.


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 Multiple Choice QuestionsShort Answer Type

267.

From a point P outside a circle, with centre O tangents PA and PB are drawn as shown in the figure, prove that

(i) ⇒AOP = ∠BOP
(ii) OP is the perpendicular bisector of AB.

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 Multiple Choice QuestionsLong Answer Type

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268. The radii of two concentric circles are 13 cm and 8 cm. AB is a diameter of the bigger circle. BD is a tangent to the smaller circle touching it at D. Find the length AD.



Given : Two concentric circles C1 and Cof radii 13 cm and 8 cm respectively. AB is a diameter of the bigger circle (C1) and BD is a tangent to the smaller circle (C2).
∴ The tangent at any point of a circle is perpendicular to the radius through the point of contact.

therefore space space OD space perpendicular space BD

Now, in right triangle BOD,  we have

OB2 = OD2 = BD2                [ Using Pythagoras theorem]

rightwards double arrow   (13)= (8)+ BD

rightwards double arrow   169 = 64 + BD2 
rightwards double arrow   BD2 = 169 - 64 
rightwards double arrow space  BD2 = 105

rightwards double arrow space space space BD space equals space square root of 105 space cm
Since, perpendicular drawn from the centre to the chord bisects the chord.

rightwards double arrow space space space space space BD space equals space DE space equals space square root of 105 space cm
rightwards double arrow space space space space BE space equals space 2 BD
rightwards double arrow space space space space space space space space space equals space 2 square root of 105 space cm

Now comma space in space increment space BOD space and space increment space BAE comma
angle BDo space equals space angle BEA space equals space 90 degree

(∵ ∠BEA = 90°, angle in semicircle is right angle] and, ∠OBD = ∠ABE     (common)

Therefore, using AAS similar condition ΔBOD ~ ΔBAE

rightwards double arrow space space BD over BE equals OD over AE

[Proportional sides of two similar triangles]

rightwards double arrow space space fraction numerator square root of 105 over denominator 2 square root of 105 end fraction equals 8 over AE
rightwards double arrow space space space 1 half equals 8 over AE
rightwards double arrow space space space space AE space equals space 16 space cm

Now, in right triangle ADE, we have

AD2 = AE2 + DE

rightwards double arrow space space AD squared space equals space 16 squared space plus space left parenthesis square root of 105 right parenthesis squared
                = 256 + 105
                = 361

rightwards double arrow     AD  = 19   cm.

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 Multiple Choice QuestionsShort Answer Type

269. In two concentric circles, prove that all chords of the outer circle which touches the inner circle are of equal length.


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270. Prove that the intercept of a tangent between two parallel tangents to a circle subtends a right angle at the centre of the circle.
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