van=facebook.com/LearningCalculus$

f(x):=x+1/x;

g(x):=x^3+1/x^3;

a:rhs(first(solve(f(x)=5,x)));float(%);

b:rhs(second(solve(f(x)=5,x)));float(%);

fullratsimp(g(a));

fullratsimp(g(b));