Prove that the length of the tangents drawn from an external point to a circle are equal, hence show that the centre lies on the bisector of the angle between the two tangents? -SST 10th

1 Answer

Answer :

Given: PT and TQ are two tangent drawn from an external point T to the circle C (O, r). To prove: 1. PT = TQ  2. ∠OTP = ∠OTQ  Construction: Join OT. Proof: We know that, a tangent to circle is perpendicular to the radius through the point of contact. ∴ ∠OPT = ∠OQT = 90° In ΔOPT and ΔOQT, OT = OT  (Common) OP = OQ  ( Radius of the circle) ∠OPT = ∠OQT  (90°) ∴ ΔOPT ΔOQT  (RHS congruence criterion) ⇒ PT = TQ  and ∠OTP = ∠OTQ (CPCT) PT = TQ, ∴ The lengths of the tangents drawn from an external point to a circle are equal. ∠OTP = ∠OTQ, ∴ Centre lies on the bisector of the angle between the two tangents.

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