x^3(square root of x + 1)
x^3 * (x + 1)^(1/2)
i'm stuck after this.
differentiate using product rule
$\displaystyle \frac{dy}{dx} = 3x^2 (x+1)^{\frac{1}{2}}+x^3\frac{1}{2}(x+1)^{\frac{-1}{2}}$
$\displaystyle = 3x^2 (x+1)^{\frac{1}{2}}+\frac{x^3}{2\sqrt{x+1}}$
$\displaystyle = \frac{6x^2 (x+1)+x^3}{2\sqrt{x+1}}$
$\displaystyle = \frac{7x^3 +6x^2}{2\sqrt{x+1}}$