kill(all)$

van=facebook.com/LearningCalculus$

Log(a,x):=log(x)/log(a);

f(x):=''(fullratsimp(expand(sqrt(Log(4,x^x)*Log(x,256)-4))));

newton(t):=float(subst(t,x,x-f(x)/diff(f(x),x)))$

newton(newton(newton(newton(1))));

float(f(1));