Answer:
Rotation of 180° about the origin transforms point (x, y) into (-x, -y). Therefore:
A (3, 1) -> A' (-3, -1)
B (5, 4) -> B' (-5, -4)
C (7, 2) -> C' (-7, -2)
D (4, 0) -> D' (-4, 0)
Length of AD = √[(3 - 4)² + (1 - 0)²] = √2
Length of A'D' = √[(-3 - (-4))² + (-1 - 0)²] = √2
