[填空题]
A function f(x) has g.gf* :z- bu3iud:ql(r (rtvazz +9pofp j0kd06a /ggderivative $f^{\prime}(x)=6 x^{2}-24 x$ . 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 $\lt$
