若X^2+XY=2,XY—Y^2=-7,则X^2+Y^2=( );X^2+3XY-2Y^2=( )

问题描述:

若X^2+XY=2,XY—Y^2=-7,则X^2+Y^2=( );X^2+3XY-2Y^2=( )

-12(2式乘以2再加上1式)