Let $X=C([0,1])$ and $T: X \rightarrow X$ defined as $$(Tf)(t)=f(t)+f(0)$$ Prove $T$ is bounded.
I was thinking about using the fundamental theorem of calculus in order to get some bounds on $f(0)$ but still don't manage to find the final result $||Tf|| \leq c ||f||$.
What about $||Tf||_X=||Tf||_\infty=\sup_{t\in[0,1]}|f(t)+f(0)|\le 2||f||_\infty=2||f||_X$? Hence, $T$ is bounded.