MathGroup Archive: March 1996 [00252]

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Re: Question : How to force ( Exp[I x]/2+Exp[-I x]/2=cos(x) ) ?

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Subject: [mg3424] Re: Question : How to force ( Exp[I x]/2+Exp[-I x]/2=cos(x) ) ?
From: Harald Berndt <haraldb at nature.berkeley.edu>
Date: Wed, 6 Mar 1996 01:47:04 -0500
Organization: University of California Forest Prodcts Lab
Sender: owner-wri-mathgroup at wolfram.com

Yeou-Jyh Tsai wrote:

>         I use Mathematica's MatrixExp to generate the symbolic form of
> a matrix's exponential. It gives me lots of
>           I x     -I x          -I x      I x
>          E      E            I E        IE
>         ---   + ------ and  -------- - -----
>          2         2            2        2
> which should be converted to Cos[x] and Sin[x], respectively. Does anyone
> know how to do this ?

Use ComplexExpand[].

Best,

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