The volume of water a spherical tank can hold is given by the next formula:

$\displaystyle V(h)= \pi h^2 \frac{3R - h}{3}$

, where:

● V is the water volume inside the tank in $\displaystyle m^3$

● R is the radius in $\displaystyle m$, and

● h is the level of water, measured from the bottom of the tank (in $\displaystyle m^3$).

I need to find out, using bisection and Newton-Raphson iterations, what the level of water has to be in order to get $\displaystyle 90m^3$ of water from a $\displaystyle 3m$ radius tank.

So basically, what i've done is find the value of $\displaystyle h$ within the formula, and apply bisection to the resulting equation. But here's the problem. The resulting formula is a 3º degree formula, so i get 3 roots (obviously bisection gives me just one, depending on the initial interval).

So the three roots are (aprox.):

●$\displaystyle 7.4526264$

●$\displaystyle 4.2565863$

●$\displaystyle - 2.7092127$

Thanks in advance.

P.S.: I'm using scilab as my numerical analysis software.