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Heron's Formula

Question
CBSEENMA9002970

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

Solution

Given: ∠AOB and ∠CO'D are the two equal angles subtended by the chords AB and CD of two congruent circles with centres O and O' respectively. (See Example 1)
To Prove: AB = CD.
Proof: In ∆OAB and ∆O'CD,
OA = O'C
| Radii of congruent circles
OB = O'D
| Radii of congruent circles
∠AOB = ∠CO'D    | Given
∴ ∆OAB ≅ ∆O'CD    | SAS Rule
∴ AB = CD.    | C.P.C.T.