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9(x+y)的平方-6(x+y)+1
人气:144 ℃ 时间:2020-03-22 21:45:23
解答
9(x+y)²-6(x+y)+1
=[3(x+y)]²-2×3(x+y)×1+1²
=[3(x+y)-1]²
=(3x-3y-1)²
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