Let $f$ be a continuous function with bounded variation on $[0,1]$.
Question: Is it true that \begin{equation*} \int_{[0,1]}f'(x)dx=f(1)-f(0) ? \end{equation*}
Let $f$ be a continuous function with bounded variation on $[0,1]$.
Question: Is it true that \begin{equation*} \int_{[0,1]}f'(x)dx=f(1)-f(0) ? \end{equation*}
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No, it is false. The Cantor function is continuous, increasing (and so it has bounded variation) and $f'(x)=0$ for $\mathcal{L}^1$ a.e. $x\in [0,1]$, so $$f(1)-f(0)=1-0>\int_0^1 f'(x)\,dx=0.$$ For the fundamental theorem of calculus to hold it is necessary and sufficient that $f$ is absolutely continuous.