Triangle abc was transformed using the rule (x, y) → (–y, x). the vertices of the triangles are shown.

a (–1, 1)
b (1, 1)
c (1, 4) a' (–1, –1)
b' (–1, 1)
c' (–4, 1)
which best describes the transformation?

the transformation was a 90° rotation about the origin.
the transformation was a 180° rotation about the origin.
the transformation was a 270° rotation about the origin.
the transformation was a 360° rotation about the origin