$\cosh(x+iy)$ splits as $\cosh x\cos y+i\sinh x\sin y$.Suggest a slogan
For \(x,y\in\RR\), \[ \cosh (x+i y) =\cosh (x) \cos (y)+i \sinh (x) \sin (y). \]
What is the angle addition formula for $\cosh(x+iy)$?
$\cosh(x+iy)$ in terms of real and imaginary parts
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