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已知m-n=3,求代数式m2-n2+2m-8n-4的值
人气：293 ℃　时间：2019-10-01 20:03:16
解答
m2-n2+2m-8n-4
=(m-n)(m+n)+2m-8n-4
=3m+3n+2m-8n-4
=5m-5n-4
=5(m-n)-4
=15-4
=11
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