answer:
x²-y²= (x+y)(x-y)
x²-y²= (x+y)(x-y)(x+y)(x-y)
x²-y²= (x+y)(x-y)(x+y)(x-y)x²+xy-xy-y²
x²-y²= (x+y)(x-y)(x+y)(x-y)x²+xy-xy-y²x²-y²
