[填空题]
A function f(x) ha ct m51mhg,-6(mk 6g0pc(cwm kvak+vw lq3i7ts derivativ 2e i5zhcrg1alb5c .k8e $f^{\prime}(x)=6 x^{2}-24 x$ . 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 $\lt$