Question

If (x+√x2+1)(y+√y2+1)=1 what is x+y?

Answer 1

(x+x+1)(y+y+1)=1

because square root get cancelled

(2x+1)(2y+1)=1

4xy+2x+2y+1=1

4xy+2x+2y=0

2x+2y=-4xy

2(x+y)=-4xy

x+y=-2xy