已知4m+n=90,2m-3n=10,求(m+2n)^2-(3m-n)^2的值
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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](/uploads/image/z/6749594-26-4.jpg?t=%E5%B7%B2%E7%9F%A54m%2Bn%3D90%2C2m-3n%3D10%2C%E6%B1%82%28m%2B2n%29%5E2-%283m-n%29%5E2%E7%9A%84%E5%80%BC)
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
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
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