x方 +2xy-1=0 则x+y的取值范围是
问题描述:
x方 +2xy-1=0 则x+y的取值范围是
如题
答
x^2+2xy+y^2-y^2-1=0
(x+y)^2=y^2+1>=1
x+y>=1或x+y