Question

Find parametric equations for the rectangular equation x2 + y2 – 25 = 0.

Answer 1

Yike... this isn't really straightforward...
First...
x² + y² = 25

Answer 2

For conversion to polar purposes,

x = r cos theta
y = r sin theta

x² + y² = 25

(r cos theta)^2 + (r sin theta)^2 = 25
r² * cos² (theta) + r² * sin² (theta) = 25

r² [(cos² (theta) + sin² (theta)] = 25

r² * 1 = 25

r² = 25

r = 5 or r = -5

Note: cos² (theta) + sin² (theta) = 1 (trig identity)