# Help: Lorentz transform for angles

1. May 7, 2005

### Lorentzf

Hi everybody,
I would need to find the lorentz transform for angles from primed to unprimed system. Could someone help fast?

Thanks a bunch, best,

Lorentzf

2. May 7, 2005

### robphy

Consider a right-triangle with legs:
x along the direction of motion and
y along a perpendicular direction.
Define tan (theta)=y/x in the frame of that triangle.
How do the legs transform?

3. May 7, 2005

### Lorentzf

Thanks, yes, that's what I do, but there are worked out formulae, with
sin(theta) as a function of tan(theta'/2) or something...
That's what I was looking for.

Thanks anyway, best,

Lorentzf

4. May 7, 2005

### jdavel

Lorentzf,

If you can't write the formula from the help that robphy gave, you don't deserve your username! ;-)

5. May 7, 2005

### Lorentzf

Dear all,
is this a place to help or to show off?
tan(theta)=(1/gamma)*tan(theta'), thanks a lot, I can see that, professors...
But there is a set of worked out, simple formulae also for the transformation of sinuses, cosinuses, etc. Of course I can do any calculation without, but they would be useful to simplify my life...

Best, anyway,

Lorentzf

6. May 7, 2005

### dextercioby

What use would it be to you knowing how the other "trigonometrical functions" would transform under a SLT...?You're interested in knowing how $\theta$ transforms,not $\tan\theta,\sin\theta,\cos\theta,\arcsin\theta,\arccos\theta,...$.

Daniel.

7. May 8, 2005

### Lorentzf

In order to simplify calculations...

Best wishes,

Lorentzf