The seventh problem is proved to be unbounded on the interval (0, 1).
Because for any M>0, the point Xo can always be found in (0, 1), so that f (XO) >; M. for example, if Xo=(k belongs to n), then f(Xo)=2kπ+, and when k is large enough, f (XO) >; M, so it is unbounded on (0, 1.
Prove again that it is not infinite.
Because Xo can always be found for any M>0, n>0, so 0