Hmmm, this is the part I was confused about because, critical points are where the function is equal to 0. When I set the function to 0, I am lost about what I am supposed to do next,
\[\dfrac{(a-b)cdx^{d-1}}{(c+x^d)^2}=0
\]
\[(a-b)cdx^{d-1}=0
\]
I thought about dividing (a-b) from both sides...