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Help needed in Mathematica

• To: mathgroup at yoda.physics.unc.edu
• Subject: Help needed in Mathematica
• From: Steve Xing Gu <sgu at henry.eecs.berkeley.edu>
• Date: Thu, 23 Jun 1994 22:43:23 -0700

	I recently encountered a problem which I cannot solve sucessfully by
Mathematica functions.  I have a transcedental function in the form(A) of
C1 Cos[X] + C2 Sin[X], and I want to use one function to convert form(A) to
the form(B), C3 Cos[X + Y].
	Converting from form(B) to form(A) can be easily done by the function,
"TrigReduce" in "Algebra`Trigonometry`", as the example shown below:
***************************************************************************
In[84]:=
N[Expand[TrigReduce[5.64 Cos[t + 3 Pi / 4]]]]
Out[84]=
-3.98808 Cos[t] - 3.98808 Sin[t]
***************************************************************************

But I've been unsucessfuly in converting from -4 Cos[t] - 4 Sin[t] to
5.64 Cos[t + 3 Pi / 4].

Handling transcedental functions is one of the weak parts of Mathematica.
I appreciate any assistance on this problem.


Steve Gu
sgu at ohm.eecs.berkeley.edu