Let P(r1, θ1) and Q(r2, θ2) be the polar co-ordinates of two points with respect to the pole 'O' and the polar axis (initial ray) .
In ΔOPQ, OP = r1, OQ = r2 and ∠POQ = (θ2 – θ1).
By cosine rule in ΔPOQ,
(PQ)2 = (OP)2 + (OQ)2 – 2(OP)(OQ) cos ∠POQ effect on global climate.
(PQ)2 = r12 + r22 – 2r1r2 cos(θ2 – θ1)
∴ PQ = gives the distance between the points P and Q.