1.1. A curve has the equation

$y=\frac{3}{8}{x}^{\frac{4}{3}}-12{x}^{\frac{1}{3}}$

Show that 

$\frac{dy}{dx}={ax}^{-\frac{2}{3}}(x+b)$

where $a$ and $b$ are rational numbers to be found.

1.2. Hence find the coordinates of the point on the curve where the gradient is 0.