8. The smaller piece can be detached, rotated and
placed into the right of the larger piece. The two
pieces together form a rectangle, whose width is
a+b and height a-b
a b
a-b
This rectangle’s area is (a + b)(a - b)
9. This rectangle’s area is same as the original figure
There for,
a2 – b2 = (a + b)(a - b)