8m(m+n)²-2m(m-n)²=2m(4(m+n)²-(m-n)²)=2m(2m+2n+m-n)(2m+2n-m+n)=2m(3m+n)(3n+m)再把m=1 n=2带入 =2（3+2）（6+1）=70
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