Question

lm+n-3l+m^2n^2+4mn+4=0 求(4m-n)(m-2n)-(n-m）(-m-n)

Answer 1

lm+n-3l+m^2n^2+4mn+4=0

lm+n-3l+(mn+2)²=0

则：

m+n-3=0

mn+2=0

解得：

m+n=3

mn=-2

m²+n²=(m+n)²-2mn=9+4=13

(4m-n)(m-2n)-(n-m）(-m-n)

=4m²-9mn+2n²+n²-m²

=3m²+3n²+18

=3(m²+n²)+18

=39+18

=57