Question

A triangle is rotated 90° about the origin. Which rule describes the transformation?

(x, y) → (–x, –y)
(x, y) → (–y, x)
(x, y) → (–y, –x)
(x, y) → (y, –x)

Answer 1

Rotation by 90° about the origin (counterclockwise) sends (x,y) to (-y,x).

Check: (1,0) → (0,1), (0,1) → (−1,0), so the rule is (x,y) → (−y,x).