Prove that If Chords of Congruent Circles Subtend Equal Angles at Their Centres, Then the Chords Are Equal. - Mathematics

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Prove that if chords of congruent circles subtend equal angles at their centres, then the chords are equal.

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Solution

Let us consider two congruent circles (circles of same radius) with centres as O and O'.

In ΔAOB and ΔCO'D,

∠AOB = ∠CO'D (Given)

OA = O'C (Radii of congruent circles)

OB = O'D (Radii of congruent circles)

∴ ΔAOB ≅ ΔCO'D (SAS congruence rule)

⇒ AB = CD (By CPCT)

Hence, if chords of congruent circles subtend equal angles at their centres, then the chords are equal.

Concept: Angle Subtended by a Chord at a Point
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Chapter 10: Circles - Exercise 10.2 [Page 173]

APPEARS IN

NCERT Class 9 Maths
Chapter 10 Circles
Exercise 10.2 | Q 2 | Page 173

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