#teste1.m
clear all
x0=12; % estimativas iniciais para x(1) e x(2)
options=optimset('Display','iter'); % mostra a solu¸c~ao em cada it.
[x,fval,exitflag,output]=fsolve('fun1',x0,options) % resolve

fun1.m
function F=fun1(x)
F(1) = x(1)^3 - (3*x(1)^2)*10 + 4000 * 0.638;