Final answer:
The rule that shows the input and output of the rotation is (x, y) → (y, -x). The new coordinate of A' is (-1, -5).
Step-by-step explanation:
When a trapezoid ABCD is rotated 90° clockwise, the rule that shows the input and output of the rotation is (x, y) → (y, -x). This means that the x-coordinate becomes the y-coordinate and the y-coordinate becomes the negative of the x-coordinate.
Given that A is at (5, -1), we can apply the rule to find the new coordinate of A':
A' = (y, -x) = (-1, -(5)) = (-1, -5).