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MathGroup Archive 1999

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Re: Solve and Trig functions

  • To: mathgroup at smc.vnet.net
  • Subject: [mg19334] Re: [mg19295] Solve and Trig functions
  • From: BobHanlon at aol.com
  • Date: Mon, 16 Aug 1999 02:15:00 -0400
  • Sender: owner-wri-mathgroup at wolfram.com

Kevin,

I assume that the intent is not to tell Mathematica the definition of Tan 
since it already knows the definition. Rather, the intent is to force it to 
use that knowledge. Consequently, I suggest you define the concept of 
dividing two equations as follows:

Unprotect[Equal];
Equal /: Equal[a_, b_]/Equal[c_, d_] := Equal[a/c, b/d];
Protect[Equal];

eq1 = a1 + b1 == Sin[fi];
eq2 = a2 + b2 == Cos[fi];

eq1/eq2 // Reverse

Tan[fi] == (a1 + b1)/(a2 + b2)

Bob Hanlon

In a message dated 8/14/99 5:45:38 AM, kevin.mccann at jhuapl.edu writes:

>If I have the following two equations:
>
>eq1 = a1 + b1 == Sin[fi];
>eq2 = a2 + b2 == Cos[fi];
>
>It is clear that
>
>Tan[fi] == (a1+b1)/(a2+b2)
>
>but how do I get Mathematica to recoginize this? This problem is trivial,
>but 
>with more complicated expressions, the answer may not be immediately 
>obvious.
>


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