Question

Given a point ( x, y
), what is the new point when the point is rotated counterclockwise about the origin 270 degrees?

Answer 1

Rotation by 270° counterclockwise (θ = 3π/2) uses the matrix
[[cosθ, -sinθ],[sinθ, cosθ]] = [[0,1],[-1,0]].
Applying this to (x,y) gives (y, −x).