kill(all)$

van=facebook.com/LearningCalculus$

f(x):=x^3-3*x-4$
g(x):=x^2+x+1$

third(solve(f(x),x));
float(%);

third(solve(f(x)=g(x),x));
float(%);

fullratsimp(f(rhs(third(solve(f(x)=g(x),x)))));
float(%);