【求完整說明及解答】中二數學題兩條

1:
　25(x + 1)² - 16(x - 1)²
= [5(x + 1)]² - [4(x - 1)]²
= [5(x + 1) + 4(x - 1)] [5(x + 1) - 4(x - 1)]
= (5x + 5 + 4x - 4) (5x + 5 - 4x + 4)
= (9x + 1) (x + 9)


2:
　m(x + y)² - 4m(x - y)²
= m [(x + y)² - 4(x - y)²]
= m {(x + y)² - [2(x - y)]² }
= m [(x + y) + [2(x - y)] [(x + y) - [2(x - y)]
= m (x + y + 2x - 2y) (x + y - 2x + 2y)
= m (3x - y) (-x + 3y)
= - m (3x - y) (x - 3y)