Solve the following problem using Lagrange multipliers. 1.) Find the critical points off(x,y)=on the curve.

Thus, yeilding my three equations with three unknowns:

Solving the equations, I get the following:

Plugging these into the third equation yeilds:

This is where I'm stuck, how can (a positive number) plus (also a positive number) = -1 when added together. Can someone help me find my mistake so I can finish the problem? Thanks