Final answer:
The measure of ∠CPC' after a 90° clockwise rotation of ∆ABC around point P to form ∆A'B'C' is 90°.
Step-by-step explanation:
When ∆ABC is rotated 90° clockwise about a point P to form ∆A'B'C', we are performing a geometric transformation of rotation. Because it's a 90° rotation, all points of ∆ABC will move to a position where they are perpendicular to their initial location in regards to point P.
Point C will move to position C', creating an angle ∠CPC'. Since the rotation is 90° clockwise and if point P is considered at the center of rotation, the measure of ∠CPC' will also be 90°. This is due to the fact that the distance from the point of rotation remains constant during a rotation, and the rotation changes the angle by exactly 90°.
In other words, ∠CPC' is the angle created at point P due to the rotation of point C to C'. As point C has been rotated 90° to reach C', the angle at P, which is ∠CPC', will measure 90°.