# Venerable Soul!

Number Theory Level 3

Find $$\sum(x+y)$$ if $$(x,y)$$ indicates the pairs that are the solutions of the equation- $(x^{2}+1)(y^2+1)+2(x-y)(1-xy)=4(1+xy)$

$$x,y \in \mathbb{Z}$$

Note-This problem is not mine. $$\sum(x+y)$$ indicates sum of all pairs satisfying the equality

×