Again, more like this
% f = 3*exp(x)-4*cos(x)
% df/dx = 3*exp(x)+4*sin(x)
i=1;
x=0.1;
err = 1;
while err>10^-8 && i<100
xold = x;
fx=3*exp(x)-4*cos(x);
fpx= 3*exp(x)+4*sin(x);
x=x-fx/fpx;
err=abs((x-xold)/x);
i=i+1;
end
disp(x)