[填空题]
A function f(x) has derivatln;+w; )hp dusp8dh -e+fl+piiv inl r:f3b6w+5sl.w bwe $f^{\prime}(x)=6 x^{2}-24 x$ . The graph of f has an x -intercept at x=1 .
1. Find f(x) .
2. The graph of f has a point of inflexion at x=k . Find k .
3. Find the values of x for which the graph of f is concave-up. x>
