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In the following figure, if OA = 5 cm, AB = 8 cm and OD is perpendicular to AB, then CD is equal to ______.

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Question

In the following figure, if OA = 5 cm, AB = 8 cm and OD is perpendicular to AB, then CD is equal to ______.

Options

  • 2 cm

  • 3 cm

  • 4 cm

  • 5 cm

MCQ
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Solution

In the following figure, if OA = 5 cm, AB = 8 cm and OD is perpendicular to AB, then CD is equal to 2 cm.

Explanation:


We know that, the perpendicular from the centre of a circle to a chord bisects the chord.

AC = CB = `1/2` AB = `1/2` × 8 = 4 cm

Given OA = 5 cm

AO2 = AC2 + OC2

(5)2 = (4)2 + OC2

25 = 16 + OC2

OC2 = 25 – 16 = 9

OC = 3 cm   ...[Taking positive square root, because length is always positive]

OA = OD  ...[Same radius of a circle]

OD = 5 cm

CD = OD – OC

= 5 – 3

= 2 cm

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Chapter 10: Circles - Exercise 10.1 [Page 99]

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NCERT Exemplar Mathematics Exemplar [English] Class 9
Chapter 10 Circles
Exercise 10.1 | Q 2. | Page 99

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