Question

Find the slope of the tangent line to the curve (a lemniscate)
2(x^2+y^2)^2 = 25(x^2-y^2)
at the point ( -3 , 1 ).

I got:
y' = 50x - (4(x^2+y^2) * 4x) / 54y
but that isn't correct, if you want more a more detailed description of what I did just ask.