Question

He cartesian coordinates of a point are given. (a) (−9, 9) (i) find polar coordinates (r, θ) of the point, where r > 0 and 0 ≤ θ < 2π.

Answer 1

Radius = 
9^2 + 9^2 = d^2
d = sqrt(162), about 12.73

theta = 
atan(9/-9)

is 45°, but in 2nd quad, so add 90

(12.727, 135°)