I need help with implicit differentiation

[KFS]

Hello. My problem is as follows: Suppose x^4+y^2+y-3=0. a) Compute dy/dx by implicit differentiation. b) What is dy/dx when x=1 and y=1? c) Solve for y in terms of x (by the quadratic formula) and compute dy/dx directly. Compare with your answer in part a).
I solved a) and b). a)=-4x^3/(2y + 1), and b)=-4/3. I'm stuck at c). This is what I've been doing: Using the quadratic formula to solve for y in x^4+y^2+y-3=0 gives y=-1±√-4x^4+13/(2). Then applying the chain rule in the result of y gives -4x^3/(√-4x^4+13). But it must give the same as a)=-4x^3/(2y + 1) . Where am I failing at? How can I solve it?
Thank you for your time.

[studiot]

Hello, KFs, and welcome to ScienceForums.

You have done some good work and congratualtions on posting your attempt.

So why not amaze yourself and finish the job?

When x = 1

[math]\frac{{ - 4{x^3}}}{{\sqrt { - 4{x^4} + 13} }} = \frac{{ - 4}}{{\sqrt { - 4 + 13} }}[/math]

Which you have already calculated.