       Re: AW: Re: Expanding Trig Power Identities

• To: mathgroup at smc.vnet.net
• Subject: [mg30402] Re: AW: [mg30365] Re: [mg30348] Expanding Trig Power Identities
• From: BobHanlon at aol.com
• Date: Wed, 15 Aug 2001 01:04:08 -0400 (EDT)
• Sender: owner-wri-mathgroup at wolfram.com

```In a message dated 2001/8/14 8:44:10 AM, Matthias.Bode at oppenheim.de writes:

>I tried Bob Hanlon's TrigReduce Table changing n from "{n, 4}" to "{n,
>1, 3,
>0.5}":
>
>Table[{y = Sin[a]*Sin[b]^n, "=", TrigReduce[y]}, {n, 1, 3, 0.5}] //
>TableForm
>
>and neither the integer nor the non-integer exponent expressions evaluated
>whereas the original example "{n, 4}" evaluates just fine. Why?
>

If the step is an approximate number then everything after the first value
(even if it is exact) is approximate.

Table[k, {k, 1, 3, 0.5}]

{1, 1.5, 2., 2.5, 3.}

The TrigReduce rules require certain forms (exact powers).  Use an exact
(rational) step

Table[{y = Sin[a]*Sin[b]^n, "=", TrigReduce[y]},
{n, 1, 3, 1/2}] //Factor // TableForm

or

Table[{y = Sin[a]*Sin[b]^Rationalize[n], "=", TrigReduce[y]},
{n, 1, 3, 0.5}] //Factor//TableForm

Bob Hanlon
Chantilly, VA  USA

```

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