Are there any cases which the First Fundamental Theorem of Calculus would fail?
First Fundamental Theorem of Calculus
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real-analysis
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0General idea is good, but too many words, hiding essential idea. Let $f(x)$ be as in your definition. Then $F(x)=\int_0^x f(t)\,dt$ exists and is $0$ for all $x$. Certainly $F(x)$ is differentiable for all $x$, but $F'(1)=0$ while $f(1)=1$. (You were asked to prove or disprove $A$ **and** $B$. You have disproved it if you show $B$ fails.) – 2012-04-05
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0Your function is certainly Riemann integrable (only countably many discontinuities). The problem with $F^\prime(1/2)$ is immediate. If $f(x)$ were in addition continuous though, the statement would hold. But isn't $f(1/2) = 1/2$? – 2012-04-05
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1A true theorem never fails. – 2012-04-06