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Use the Mean Value Theorem to estimate the value of $\sqrt{80}$.

and

how should we take $f(x)$?

Thanks in advance.

Regards

1 Answers 1

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You want to estimate a value of $f(x) = \sqrt{x}$, so that's a decent place to start. The mean value theorem says that there's an $a \in (80, 81)$ such that \frac{f(81) - f(80)}{81 - 80} = f'(a). I don't know what $a$ is, but you know $f(81)$ and you hopefully know how to write down f'. How small can f'(a) be?

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    excelent!! thanks so much =)2011-08-18