Using the definition of \(\cosh x\) and the Maclaurin series expansion of \(\mathrm { e } ^ { x }\), find the first three non-zero terms in the Maclaurin series expansion of \(\cosh x\).
10
Hence find a trigonometric function for which the first three terms of its Maclaurin series are the same as the first three terms of the Maclaurin series for cosh (ix). [0pt]
[3 marks]
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