5x2-3xy-4y2-11xy+(-7x2)-(-2y2),其中x2+y2=7,xy=-2,求值
问题描述:
5x2-3xy-4y2-11xy+(-7x2)-(-2y2),其中x2+y2=7,xy=-2,求值
答
5x2-3xy-4y2-11xy+(-7x2)-(-2y2),
=5x2-3xy-4y2-11xy-7x2+2y2
=-2x2-14xy-2y2
=-2(x2+y2)-14xy
=-14+28
=14