Why does applying trigsimp aid solvability?

Are you asking  "why doesn't solve always call trigsimp first?"

Perhaps because it can be an enormous waste of time.

But maybe solve can tell when it is a good idea and apply it only then.
What criteria would you use?

There are a large number of transformations that are possible, and 
picking the wrong
one can be very expensive.

RJF



Paul Richards wrote:
> 2009/6/11 Stavros Macrakis <macrakis at alum.mit.edu>:
>   
>> On Thu, Jun 11, 2009 at 4:20 PM, Paul Richards <paul.richards at gmail.com>
>> wrote:
>>     
>>> PS. How do I better copy/paste maxima output into email?  I have a
>>> feeling this is only viewable with fixed width fonts.
>>>       
>> If you set
>>    display2d:false$
>> you will get output that doesn't depend on fixed-width fonts etc.
>>
>>     
>
> Thanks.
>
> Here are those expressions again:
>
> (%i2) c^2 = (cos(a/r) - 1)^2 + sin(a/r)^2;
>
> (%o2) c^2 = sin(a/r)^2+(cos(a/r)-1)^2
> (%i3) solve(%i2, a);
>
> (%o3) [sin(a/r) = -sqrt(-cos(a/r)^2+2*cos(a/r)+c^2-1),
>        sin(a/r) = sqrt(-cos(a/r)^2+2*cos(a/r)+c^2-1)]
> (%i4) solve(trigsimp(%i2), a);
>
> solve: using arc-trig functions to get a solution.
> Some solutions will be lost.
> (%o4) [a = (%pi-acos(c^2/2-1))*r]
>
>
> So my question is still, why does applying "trigsimp" give be a better
> answer from "solve"?
>
>