已知m^2+2mm=484,3mm+2n^2=560,求代数式2m……2=13mn+6n^2-440
问题描述：
已知m^2+2mm=484,3mm+2n^2=560,求代数式2m……2=13mn+6n^2-440
答
2m^2+13mn+6n^2-440
=(2m^2+4mn)+(9mn+6n^2)-440
=2(m^2+2mn)+3(mn+2n^2)-440
=2x484+3x560-440
=2208