(x + 2y)² + (x - y)²
((x + 2y)(x + 2y)) + ((x - y)(x - y))
(x(x + 2y) + 2y(x + 2y)) + (x(x - y) - y(x - y))
(x(x) + x(2y) + 2y(y) + 2y(2y)) + (x(x) - x(y) - y(x) + y(y))
(x² + 2xy + 2xy + 4y²) + (x² - xy - xy + y²)
(x² + 4xy + 4y²) + (x² - 2xy +y²)
(x² + x²) + (4xy - 2xy) + (4y² + y²)
2x² + 2xy + 5y²
