Re: a question about complex variable

• To: mathgroup at smc.vnet.net
• Subject: [mg21646] Re: a question about complex variable
• From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
• Date: Fri, 21 Jan 2000 03:59:56 -0500 (EST)
• Organization: Universitaet Leipzig
• References: <200001170343.WAA13446@smc.vnet.net> <8615hh\$jtk@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

```ZHU Xiaopeng wrote:
>
> In my algebra computation, I obtain a expression:
> C = (- I Cos[2 P] - Sin[2 P]) Tan[A]
> P,A are real variables. Apperently, the argument of C is -2(P+Pi/4) and the
> absolute value of C is Tan[A]. But when I use Arg[C] and Abs[C], Mathematica
> tells me:
>
> Out[41]=Abs[(-I Cos[2 P] - Sin[2 P]) Tan[A]]
> Out[42]=Arg[(-I Cos[2 P] - Sin[2 P]) Tan[A]]
>
> This problem appeared at beginning of the computation. I have no idea to deal
> with it, so the expressions become longer and longer during the computation.
> Can somebody help me?

Hi,

In[]= cc = (-I Cos[2 P] - Sin[2 P]) Tan[A]

In[]= FullSimplify[Abs[cc], Element[{A, P}, Reals]] // InputForm
Out[]= Abs[Tan[A]]

Until you don't know the value of A>Pi/2 or not, no one can calculate
the argument.

Hope that helps
Jens

```

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