If PT is a tangent to a circle with centre O and PQ is a chord of the circle such that ∠ QPT = 70o, then find the measure of ∠ POQ.
We know that the radius and tangent are perpendicular at their point of contact.
<OPT = 90°
Now, <OPQ = <OPT – <TPQ = 90° – 70° = 20°
Since OP = OQ as both are radius
<OPQ = <OQP = 20° (Angles opposite to equal sides are equal)
Now, In isosceles <POQ
<POQ + <OPQ + <OQP = 180° (Angle sum property of a triangle)
<POQ = 180° – 20° – 20° = 140°