` a) ` ` x^2 + 10x + 25 = (x + 5)^2 `
` b) ` ` 16x^2 - 48x + 36 = (4x - 6)^2 ` hay ` = 4(2x - 3)^2 `
` c) ` ` x^2 - 4xy + 4y^2 = (x - 2)^2 `
` d) ` ` (x - 7)(x + 7) = x^2 - 49 `
Áp dụng 3 HĐT:
` a^2 + 2ab + b^2 = (a + b)^2 `
` a^2 - 2ab + b^2 = (a - b)^2 `
` a^2 - b^2 = (a - b)(a + b) `