|PS| = |SR| (If two tangents are drawn from an external point of the circle, then they are of equal lengths)∴ ∆PSR is isosceles∠PSR + ∠SRP + ∠SPR = 180∘ (sum of angles in a triangle)Since |PS| = |SR|; ∠SRP = ∠SPR⇒ ∠PSR + ∠SRP + ∠SRP = 180∘∠PSR + 2∠SRP = 180∘36∘ + 2∠SRP = 180∘2∠SRP = 180∘ - 36∘2∠SRP = 144∘
∠SRP = 2144∘=72∘
∠SRP = ∠PQR (angle formed by a tangent and chord is equal to the angle in the alternate segment)