Question

已知（x+my) (x+ny)=x^2+2xy -8y^2,求mn（m+n)的值 求过程和解释

Answer 1

（x+my) (x+ny)
=x^2+(m+n)xy+mny^2
=x^2+2xy -8y^2
所以m+n=2
mn=-8
所以mn(m+n)=-8×2=-16

Answer 2

（x+my) (x+ny)
=x^2+xy*(m+n)+mn*y^2
=x^2+2xy -8y^2

m+n=2
m*n=-8

mn（m+n)
=-8*2
=-16