[填空题]
A function f(x) has d0g 6 6nrgx k/wp5qn5 tjw f4b;z-myl/gerivatz)7ad 2ypgxy-ive $f^{\prime}(x)=6 x^{2}-24 x$ . 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 $\lt$
