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=( )
答
-12(2式乘以2再加上1式)
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)