- #1
bloynoys
- 25
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Homework Statement
Prove or disprove:
Suppose f:[a,b]->R is continuous. If f is diff on interval (a,b) and f'(x) has a limit at b, then f is diff at b.
Homework Equations
We say that f is differentiable at x0 to mean that there exists a number A such that:
f(x)=f(x0)+A(x-x0)+REM
where,
lim(x->x0) REM(x)/(x-x0) = 0
The Attempt at a Solution
We will prove f is diff at b by showing that that there exists a number A so that f(x)=f(b)+A(x-b)+REM
so,
lim(x->x0) REM(x)/(x-b) = 0
I have gotten good at normal proofs in this course and am very confused on how to build proofs with this diff theorem. I know that this is true, but am confused how to fashion the plan and how to start the proof. How do I establish the existence of an A that satisfies this?
Thanks!