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分解因式:9-x²;已知4m+n=90,2m-3n=10,求(m+2n)²-(3m-n)²的值
人气:170 ℃ 时间:2019-08-24 06:09:39
解答
9-x²
=(3+x)(3-x)
(m+2n)²-(3m-n)²
= (m+2n+3m-n)(m+2n-3m+n)
=(4m+n)(-2m+3n)
=-(4m+n)(2m-3n)
=-90×10
=-900
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