# hyperbolic cosine and sine: evaluate

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• Sep 15th 2011, 08:59 PM
freestar
hyperbolic cosine and sine: evaluate
If $cosh(t) = 5$ & $cosh(u) = 7$
What is the value of $coth(t) - tanh(u)$

I know the formulas for them but I am just getting lost. Any help would be highly appreciated! I know the cosh, sinh and tanh formulas involving $e^x$ and coth would just be the tanh formula flipped. Very lost.
• Sep 15th 2011, 09:05 PM
pickslides
Re: hyperbolic cosine and sine: evaluate
Use $\displaystyle \tanh^2 x +sech^2x = 1$ and

$\displaystyle sech x = \frac{1}{\cosh x}$