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Re: Abs and derivative problems


sylvan wrote in message <71q9qu$j25 at smc.vnet.net>...
>I could not calculate the modulus of  a complex expression containing
>imaginary parts in both denominator and numerator with Mathematica. An
>Example:
>
>(a + I b) / (c + I d)
>
>a,b,c,d (real) symbolic variables.
>
>.................

sylvan:

ComplexExpand[Abs[(a + I b)/(c + I d)], TargetFunctions -> {Re, Im}]

Out[20]=
Sqrt[a^2 + b^2]/Sqrt[c^2 + d^2]

Allan

---------------------
Allan Hayes
Mathematica Training and Consulting
www.haystack.demon.co.uk
hay at haystack.demon.co.uk
Voice: +44 (0)116 271 4198
Fax: +44 (0)870 164 0565




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