已知m^2-mn=20,mn-n^2=-12,求正式m^2-n^2与m^2-2mn+n^2的值!(请说明原因!)
问题描述：
已知m^2-mn=20,mn-n^2=-12,求正式m^2-n^2与m^2-2mn+n^2的值!(请说明原因!)
答
m^2-mn=20
mn-n^2=-12
两式相加得
m^2-n^2=20-12=8
m^2-mn=20
mn-n^2=-12
两式相减得
m^2-2mn+n^2=20+12=32