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MathGroup Archive 2004

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Re: Trig identity oscillations

  • To: mathgroup at smc.vnet.net
  • Subject: [mg47710] Re: Trig identity oscillations
  • From: adam.smith at hillsdale.edu (Adam Smith)
  • Date: Fri, 23 Apr 2004 02:30:38 -0400 (EDT)
  • References: <c67q7l$gum$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

You are correct that Cos[t+5 Pi/6]/Sin[t+Pi/3] = 1.

What is happening is that the Plot function is numerical.  As is
substitutes in various values for t you end up with a very small
number divide by another very small number.  The rounding that occurs
in the numerical evaluations is what causes the unexpected behavoir.

Try Simplify[Cos[t+5 Pi/6]/Sin[t+Pi/3]] and you will find that
Mathematica returns the expected 1.  In general it is useful to
simplify any complicated function before plotting.

Plot[Simplify[Cos[t+5 Pi/6]/Sin[t+Pi/3]],{t,0,2 Pi}]

Adam Smith



mathma18 at hotmail.com (Narasimham G.L.) wrote in message news:<c67q7l$gum$1 at smc.vnet.net>...
> Should it not be a more placid -1 ?
> Plot[Cos[t+5 Pi/6]/Sin[t+Pi/3],{t,0,2 Pi}]


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