⑴25x²—16y² (2)(a—b)(x—y)—(b—a)(x+y) (3)a²—4ab+4b² (4)4+12(x—y)+9(X—y)²
题目
⑴25x²—16y² (2)(a—b)(x—y)—(b—a)(x+y) (3)a²—4ab+4b² (4)4+12(x—y)+9(X—y)²
答案
25x²—16y²
=(5x)^2-(4y)^2
=(5x+4y)(5x-4y)
(a—b)(x—y)—(b—a)(x+y)
=(a—b)(x—y)+(a-b)(x+y)
=(a-b)(x-y+x+y)
=2x(a-b)
a²—4ab+4b²
=(a-2b)^2
=(a-2b)(a-2b)
4+12(x—y)+9(X—y)²
=[(3(x-y)+2]^2
=[(3(x-y)+2][(3(x-y)+2]
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