Find equation of tangent line to 2(x² + y²)² = 25(x² - y²) at (3,1)

I simply the equation to 2x^4 + 2y^4 = 25x^2 - 25y^2
I took derivative using implicit and got (50x - 8x^3) / (8y^3 + 50y)
I substitute in x and y values and got 33/29 as a slope, the book has a different answer.

The first step wasn't quite right.
(x^2 + y^2)^2 is NOT equal to (x^4 + y^4)

Take the derivative of both sides of the equation with respect to x.
You will get something like 4(x^2+y^2)(2x+2y*dy/dx) = 25(2x-2y*dy/dx).
Rearrange the equation, express the equation as dy/dx = something,
and then substitute (3,1) in to the equation to find the slope.