Zeros of a function using Newton or Bisection method

Hello, I am trying to find the zeros of a multivariable function (3 variables) using the Newton method or the bisection method; but I don't know where to begin. Do I need to calculate myself the partial derivatives of the function (it seems pretty impossible) or is there a simpler way to to do it ?

Here's the function:

 function [y]=Fasterisque(v,Theta,indice,Rho,S,Cx,f0,f2,mveh,g,Ethatrans,R,Omega,Cmax)

   F1=Faero(Rho,S,Cx,v);

   F2=Frlt(f0,f2,mveh,g,Theta,v);

   F3=Fgrav(m,g,Theta);

   F4=Fmotmax(Ethatrans,indice,R,v,Omega,Cmax);

   y=F1+F2+F3-F4;

end

As you can see, a "bruteforce" approach might be kinda hopeless... Thanks in advance !