In the given figure, O is the centre of a circle. PT and PQ are tangents to the circle from an external point P. If ∠TPQ=70°, find ∠TRQ.
Construction: Join OT and OQ.
OT and OQ are perpendicular to PT and PQ [Since radii are perpendicular to the tangents.]
In quadrilateral OTPQ,
∠OTP+∠TPQ+∠OQP+∠TOQ=360°⇒90°+70°+90°+∠TOQ=360°⇒∠TOQ=110°
Hence, ∠TRQ=12∠TOQ=55°(Inscribed angle theorem)