Question

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

Answer 1

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