# Cos and sin relations

1. Aug 31, 2009

### Somefantastik

if

$$\mu = cos(\theta)$$ and $$\mu_{0} = cos(\theta_{0})$$

and

$$cos(\pi - \Theta) = \mu_{0}\mu + \sqrt{1-\mu_{0}^{2}}\sqrt{1-\mu^{2}}cos(\phi)$$

Then

$$cos(\pi - \Theta) = cos(\theta_{0})cos(\theta) + sin(\theta_{0})sin(\theta)cos(\phi)$$

Is this not correct?

2. Aug 31, 2009

### g_edgar

What if one of the sines is negative?

3. Aug 31, 2009

### Somefantastik

sorry, range of $$\theta$$ is 0 to 60 degrees, and $$\theta_{0}$$ range is 0 to 70 degrees. As far as I can tell, sin will always be positive. But regardless, sin(theta)< 0 would change the value of the over all equation, but are the two equations not equal?

4. Aug 31, 2009

### Elucidus

Several questions:

(1) Are $\theta$ and $\Theta$ the same variable?

(2) What is $\phi$?

(3) I'm not sure what the equation is getting at. It appears to be a hyrid of a cofunction, symmetric, and angle sum identity. Something feels missing. Could you provide more detail as to what you are trying to show here?

--Elucidus

5. Aug 31, 2009

### Integral

Staff Emeritus
Yes, your final relationship follows from what you have given.

6. Sep 1, 2009

### Somefantastik

Ok thanks Integral; I just wanted to make sure I wasn't crazy