Question

Triangle XYZ is rotated 90° counterclockwise about the origin.

On a coordinate plane, triangle X Y Z has points (1, 3), (4, negative 1), (1, negative 1).

What are the coordinates of point Y’?
(4, –2)
(1, 4)
(–4, 1)
(–1, –4)

Answer 1

Y = (4, −1). A 90° counterclockwise rotation about the origin sends (x,y) → (−y, x). So Y' = (−(−1), 4) = (1, 4).