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Question about trig simplify
*To*: mathgroup at smc.vnet.net
*Subject*: [mg71099] Question about trig simplify
*From*: Robert Pigeon <robert.pigeon at videotron.ca>
*Date*: Wed, 8 Nov 2006 06:08:16 -0500 (EST)
Hello all,
Is this a bug?
2*Sin[a]*Cos[a] // Simplify gives Sin[2 a] as expected.
But
-2*Sin[a]*Cos[a] // Simplify gives -2*Cos[a]*Sin[a] ...... Why?
If I do -2*(Sin[a]*Cos[a]) // Simplify I get the same answer.
This comes from the rotation matrix: r = {{Cos[a],Sin[a]},{-Sin[a],Cos[a]}}.
Then I do: r.r // Simplify. That gives: {{Cos[2 a],Sin[2 a]},{-2 Cos[a]
Sin[a],Cos[2 a]}}. It does not matter if I do a FullSimplify instead of
Simplify.
After if I do r.r.r // Simplify. The answer is simplified correctly.
I am using Mathematica 5.2 on Windows XP Home.
Any idea?
Robert
Robert Pigeon
TZ = -5
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