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

A 90° rotation about the origin is usually taken to mean counterclockwise. Under this rotation, a point (x,y) moves to (-y,x); for example, (1,0) moves to (0,1). So the correct choice is B, (x,y) → (-y,x).

AI-written and checked against the verified answer.