Answer
a) $x(x+y)-y(x+y)$
b) $(x+y)(x-y)$
Work Step by Step
a) We write the area of the shaded blue region as the difference between the area of the big rectangle and the area of the white rectangle:
$$x(x+y)-y(x+y).$$
b) We factor the expression:
$$x(x+y)-y(x+y)=(x+y)(x-y).$$
