Question

find all points on the curve x^2y^2+xy=2 where the slope of the tangent line is -1

I know that you have to find the derivative when it equals -1
i got

y'=(2x*y^2-y)/(2x^2*y+x)
(i don't know if it is correct or not)

but i don't know how to go from here. any help would be good

Thanks