Question

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

R (1, 1)
S (3, 1)
T (1, 6) R' (–1, –1)
S' (–3, –1)
T' (–1, –6)
Which best describes the transformation?

The transformation was a 90° rotation about the origin.
The transformation was a 180° rotation about the origin.

Answer 1

The transformation (x, y) → (−x, −y) is a 180° rotation about the origin.

Reason: A 180° rotation sends each point (x,y) to (−x,−y) (e.g. (1,1) → (−1,−1)). A 90° rotation would send (x,y) to (−y,x) or (y,−x), which does not match these images.