实数x,y满足x≥y≥1和2x2-xy-5x+y+4=0,则x+y=_.
问题描述:
实数x,y满足x≥y≥1和2x2-xy-5x+y+4=0,则x+y=______.
答
∵2x2-xy-5x+y+4=0
∴x2+x2-xy-4x-x+y+4=0
∴x2-4x+4+x(x-y)-(x-y)=0
∴(x-2)2+(x-y)(x-1)=0
∵(x-2)2≥0,x≥y≥1,
∴(x-y)(x-1)≥0
因此两项都非负,只能都为0
∴x=y=2
∴x+y=4.
故答案为:4.