举报
cc2906
(x + y)² + 4xy= x² + 2xy + y² + 4xy = x² + 6xy + y² = x² + 6xy + 9y² - 8y² = (x + 3y)² - (√8y)² = (x + 3y + 2√2y)(x + 3y - 2√2y) (x + y)² - 4(x + y - 1) = (x + y)² - 4(x + y) + 4 = [(x + y) - 2]² = (x + y - 2)² (x - 1)(x - 3) + 1 = x² - 4x + 4 = (x - 2)²