Re: Rewriting of Trigonometric Functions
- To: mathgroup at smc.vnet.net
- Subject: [mg26843] Re: Rewriting of Trigonometric Functions
- From: "Paul Lutus" <nospam at nosite.com>
- Date: Thu, 25 Jan 2001 01:13:21 -0500 (EST)
- References: <94m8st$3mn@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
"Thomas Engelhardt" <thomas-a.engelhardt at t-online.de> wrote in message news:94m8st$3mn at smc.vnet.net... > Dear Mathgroup members, > > I have just started to use Mathematica and directly ran into a problem: > > I have rather lengthy expressions resulting from putting a sum of two > sinusodial swings to the power of three (Two-tone Intermodulation). > In order for me to recognise the contained frequencies I want Mathematica to > rewrite the contained Trigonometric functions in certain ways, namely like: > > [sin(a)]^2 should be transformed into 1/2*(1+cos2x) > and for higher powers accordingly. > > Furthermore: > sin(a)*sin(b) should be changed to 1/2*[cos(a-b) - cos(a+b)] > > I have tried all kinds of "Expand" and "Trig..." operations but Mathematica > always keeps the powers on the trigonometric functions and doesn't change > the multiplications either. > > Does anybody have an idea how I can get Mathematica to transform the > expressions in the desired way? Why not write your own functions and use them instead of the default functions? This is by far the simplest way to get a non-standard treatment of the described functions. -- Paul Lutus www.arachnoid.com