Math Forum :: View topic – condition for single-variable Inverse Function Theorem

condition for single-variable Inverse Function Theorem
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Koala

Frequent VisitorJoined: 07 Mar 2004Posts: 36

Posted: Sun Feb 06, 2005 3:53 pm    Post subject: condition for single-variable Inverse Function Theorem

Let be strictly monotonic on , differentiable at , and .
Is it true that is differentiable at ?

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Andy

Frequent VisitorJoined: 28 Oct 2003Posts: 391

Location: Hong Kong

Posted: Sun Feb 06, 2005 4:29 pm    Post subject:

Yes. For convenience, let the inverse of f be g and f(0) = c.

As f is monotone near 0, holds when y is close to c. Therefore, we have

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Koala

Frequent VisitorJoined: 07 Mar 2004Posts: 36

Posted: Sun Feb 06, 2005 6:05 pm    Post subject:

Thank you Andy. I should be more precise by asking in this way:

Is always an interior point of the domain of ?

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