Given that
$$\sinh ( A + B ) = \sinh A \cosh B + \cosh A \sinh B$$
express \(\sinh ( m + 1 ) x\) and \(\sinh ( m - 1 ) x\) in terms of \(\sinh m x , \cosh m x , \sinh x\) and \(\cosh x\)
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Hence find the sum of the series
$$C _ { n } = \cosh x + \cosh 2 x + \cdots + \cosh n x$$
in terms of \(\sinh x , \sinh n x\) and \(\sinh ( n + 1 ) x\)
Do not write
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