kill(all)$

van=facebook.com/LearningCalculus$

f(x):= 1/sqrt(x+7/2) - 1/x^2 + 7/2$

f(1/2);

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

newton(newton(-0.4952622667985183));

f(%);