function [xn,err,n] =newton(x0, tol, maxiter)
xn(1) = x0;
n=1;
err(1)=tol+1;
while (err(n)>tol) & (n<=maxiter)
    n=n+1;
    xn(n)=xn(n-1)-f(xn(n-1))/flinha(xn(n-1));
    err(n)=abs((xn(n)-xn(n-1))/xn(n));
end
end
function y=f(x)
y=x*x*x-2*x*x-5;
end
function y=flinha(x)
y=3*x*x-4*x;
end
return