Answer:
C
Step-by-step explanation:
pythagorean theorem: a²+b² = c²
area of square = length²
c = side opposite right angle = length of square Z
thus, area of square Z = c²
area of square X = a² (or b², it doesn't matter)
area of square Y = b² (or a²)
a² + b² = c²
region x + region y = region z
