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MathGroup Archive 2004

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Re: How to solve a simple Trig cofunction?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg50517] Re: [mg50500] How to solve a simple Trig cofunction?
  • From: DrBob <drbob at bigfoot.com>
  • Date: Thu, 9 Sep 2004 05:17:28 -0400 (EDT)
  • References: <200409080914.FAA08518@smc.vnet.net>
  • Reply-to: drbob at bigfoot.com
  • Sender: owner-wri-mathgroup at wolfram.com

eqn = Cos[x + 4] == Sin[3x + 2];
Reduce[eqn && 0 ? x ? Pi/2, x];
x /. ToRules[%]
%/Degree//N

(1/2)*(-3 + 2*Pi - 2*ArcTan[1 + Sqrt[2]])
26.556330730376516

The symbolic answer is in radians (if evaluated) but the numeric one is in degrees.

Bobby

On Wed, 8 Sep 2004 05:14:59 -0400 (EDT), Brian Feeny <bfeeny at mac.com> wrote:

> Lets say I have:
>
> cos[X+4] = sin[3X+2]
>
> What would be the proper way to solve the above, for X, in
> Mathematica, with the answer in degrees?
>
> I did this, but something tells me their has to be a better way:
>
> NSolve[Cos[X Degree +4 Degree] = Sin[3 X Degree+2 Degree], X]
>
> I mean, I wish i didn't have to enter "Degree"so many times, perhaps
> their is a simple way to just tell it the whole thing is in Degree.
>
> Additionally, is their a way to constrain the above to 90 > X > 0?  I
> tried doing like:
>
> NSolve[Cos[X Degree +4 Degree] = Sin[3 X Degree+2 Degree], X /; 90
>> X>0]
>
> but that obviously is not the right way since that doesn't work.
> Appreciate all the help.
>
> Brian
>
>
>



-- 
DrBob at bigfoot.com
www.eclecticdreams.net


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