已知4m+n=90,2m-3n=10,求(m+2n)^2-(3m-n)^2的值_数学解答

已知4m+n=90,2m-3n=10,求(m+2n)^2-(3m-n)^2的值

人气：210 ℃　时间：2019-08-22 19:38:20

解答

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