(i) Distance between two points P (x1, y1) and Q (x2, y2), is
√(x2 – x1)
2
+ (y2 – y1)
2
.
(ii) If points are (r1 , θ1) arid (r2, θ2), then distance between them is
√r2
1 + r2
2 – 2r1r2cos(θ1 – θ2).
(iii) Distance of a point (x1, y1) from the origin is √x2
1 + y2
1.