something I think is true but can't prove
 

Hi,


does anyone know if



sinAcosx - sinxcosA = 0 is true


if and only if sinA = sinx and cosx = cosA are true?



I've tried to prove it. I don't think I can. My mind's not working right anyway.


I thought some help with this might help me straighten my head out a bit.


(it would be appreciated).

[QUOTE=wildrabbitt;514994]Hi,


does anyone know if



sinAcosx - sinxcosA = 0 is true


if and only if sinA = sinx and cosx = cosA are true?



I've tried to prove it. I don't think I can. My mind's not working right anyway.


I thought some help with this might help me straighten my head out a bit.


(it would be appreciated).[/QUOTE]Just rename sinA = sinx = E, and cosA = cosx = F

And you get this: EF - EF = 0

sin(A)cos(x) - cos(A)sin(x)=sin(A-x)
and sin(A-x)=0 if and only if A-x is an integer multiple of π.
Good luck with your head! :smile:

thanks.

[QUOTE=Nick;514998]sin(A)cos(x) - cos(A)sin(x)=sin(A-x)
and sin(A-x)=0 if and only if A-x is an integer multiple of π.
Good luck with your head! :smile:[/QUOTE]

Or, in terms the way the OP phrased it, tan x = tan A if sin x = sin A and cos x = cos A, or if sin x = -sin A and cos x = -cos A.

[QUOTE=ewmayer;515320]Or, in terms the way the OP phrased it, tan x = tan A if sin x = sin A and cos x = cos A, or if sin x = -sin A and cos x = -cos A.[/QUOTE]

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