因式分解."
已知: 1 – a2 – b2 – 2ab
求解: 我们需要因式分解 1 – a2 – b2 – 2ab
解答:
1 – a2 – b2 – 2ab
= 1 - (a2 + b2 + 2ab)
利用 (x + y)2 = x2 + y2 + 2xy,
= 1 - (a + b)2
= 12 - (a + b)2
利用 x2 - y2 = (x + y)(x - y)
= (1 + (a + b)) (1 - (a + b))
= (1 + a + b) (1 - a - b)
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