若X-Y=根号5,XY=2,求4-(xy-3x+5y)+(x+y-xy)的值.

问题描述:

若X-Y=根号5,XY=2,求4-(xy-3x+5y)+(x+y-xy)的值.

原式=4-xy+3x-5y+x+y-xy
=4-2xy+4(x-y)
=4-2×2+4×√5
=4√5