已知x+y-z=-1,x²+y²-z²=-11,那么﹙2x-y²+2y﹚-﹙x²-z²﹢2z﹚=?

问题描述:

已知x+y-z=-1,x²+y²-z²=-11,那么﹙2x-y²+2y﹚-﹙x²-z²﹢2z﹚=?

倇RanLetter}W元

x²+y²-z²=-11
y²=-x²+z²-11
﹙2x-y²+2y﹚-﹙x²-z²﹢2z﹚
=2x+x²-z²+11+2y-x²+z²-2z
=2x+2y-2x
=2(x+y-z)
=-2