How can I solve a truss system using a system of linear equations in a function?

I am confused on how to use the bisection method to solve for F with AC being 4000N.

Bisection method example:

function [ x,N ] = Bisection( Fun,a,b,Tol )

%Find root of a function with the bisection method

% Fun should be a function containing an equation and its derivative

N = 0;

[fa dfdx] = Fun(a);

while b-a > Tol

c = 0.5*(a+b);

[fc dfdx] = Fun(c);

if fa*fc > 0

a=c;

else

b=c;

end

N=N+1;

end

x = c;

end

Anything helps