jelaskan maksud contoh soal diatas (caranya) terimakasih yg jelas dan mudah dimengerti

a) (x+y)²=(x+y)(x+y)
=x²+xy+xy+y²
=x²+y²+2xy

b) (x-y)²=(x-y)(x-y)
=x²-xy-xy+y²
=x²+y²-2xy

c) (x+y)² + (x-y)²
=(x²+y²+2xy) + (x²+y²-2xy)
=2x²+2y²+2xy-2xy
=2x²+2y²
=2(x²+y²)

d) (x+y)² - (x-y)²
=(x²+y²+2xy) - (x²+y²-2xy)
=x²-x²+y²-y²+2xy+2xy
=4xy