1 I need to know the convergence of this series

$\displaystyle \sum_{k=1}^{\infty} \frac{2k+5}{\sqrt{3{k^3} - 1/2}}$

2 I have to obtain the expression of dy/dx for the following function

3xy - 2x^2y + y^3 =0

3 $\displaystyle 5x^2 + 3y^2 = 16$

The x radius is $\displaystyle \sqrt{5}$ ?

Thanks