题目

已知x≠y,x²-x=5,y²-y=5,求x+y+7的值

提问时间：2020-10-30

答案

∵x²-x=5,y²-y=0∴(x²-x)-(y²-y)=0x²-x-y²+y=0(x²-y²)-(x-y)=0(x+y)(x-y)-(x-y)=0(x+y-1)(x-y)=0∵x≠y∴x-y≠0∴x+y-1=0即x+y=1∴x+y+7=(x+y)+7=1+7=8