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