[SPLIT] Show that u1,u2∈Su1,u2 \in S are

[SophieToft]

I got a third a final question:

3) Show that $\displaystyle u_1,\,u_2\, \in\, S$ are $\displaystyle \left\|\,\int_{u_1} ^{u_2}\, f(u)\, dt\,\right\|\,\, \leq\,\, \left|\, \int_{u_1} ^{u_2}\, ||\,f(u)\,||\, dt\,\right|$.

I know that I'm suppose to use Riemann sums and show that f is integreatable at interval [u1, u2]. But from there I'm not sure what to do.

Any ideas?

Sincerley Yours
Sophie Toft