What is the rule for finding coordinates after a 90 degree rotation?

Question

after a 180 degree rotation? after a 270 degree rotation?

Answer 1

Assume a circle with a radius of i(r=1)

@ 0 Degrees: = 1, and Y = 0.

@ 90 Degrees: X = 0, and Y = 1.

@ 180 Degrees: X = -1, and Y = 0.

@ 270 Degrees: X = 0, and Y = -1.