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MathGroup Archive 2007

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Re: Solving periodic functions

  • To: mathgroup at smc.vnet.net
  • Subject: [mg74969] Re: [mg74935] Solving periodic functions
  • From: János <janos.lobb at yale.edu>
  • Date: Fri, 13 Apr 2007 02:01:20 -0400 (EDT)
  • References: <200704120846.EAA24338@smc.vnet.net>

On Apr 12, 2007, at 4:46 AM, David Rees wrote:

> This is probably totally elementary, but I'm stumped nonetheless.
>
> Anyway, in Mathematica, how do I solve an equation with multiple 
> periodic
> functions within a given function domain bound?
>
> i.e. How would I find all values of x given 6Cos[x]-5Cos[x] = 0 =
where
> 0<x<=2Pi ?
>
> thanks
>
>

Me as a newbie, I would start with Reduce.

In[2]:=
Reduce[{6*Cos[x] -
      5*Sin[x] == 0,
    Inequality[0, Less, x,
     LessEqual, 2*Pi]}, x]
Out[2]=
x == 2*Pi + 2*ArcTan[
       (1/6)*(-5 - Sqrt[
          61])] ||
   x == 2*ArcTan[(1/6)*
       (-5 + Sqrt[61])]

J=E1nos


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