Let $$y^4 + 5x = 21.$$ What is the value of $d^2y/dx^2$ at the point $(2, 1)$?
I’m stuck at trying to work out the second implicit derivative of this function. As far as I can work out, the first derivative implicitly is
How do you take the second derivative implicitly with respect to $x$ when $x$ has vanished? There would be nowhere to plug in $x=2$. What am I missing here?