4m+n=90
2m-3n=10 得:-(2m+3n)=-10
(m+2n)^2-(3m-n)^2
=[(m+2n)+(3m-n)][(m+2n)-(3m-n)]
=(4m+n)(-2m+3n)
=90x(-10)
=-900
已知4m+n=90,2m-3n=10,求(m+2n)^2-(3m-n)^2的值
已知4m+n=90,2m-3n=10,求(m+2n)^2-(3m-n)^2的值
数学人气:653 ℃时间:2019-08-22 19:38:20
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