# What is the name of this formula?

There is 3d angle addition formula for which I would like to know what it is called in the literature:

Given two vectors $\vec v_1$, $\vec v_2$ at (physicist's) angles $(\theta_1,\,\phi_1)$ and $(\theta_2,\,\phi_2)$, the angle $\Theta$ between the two vectors is given by:

$$\cos \Theta=\cos \theta_1 \cos\theta_2+\sin\theta_1\sin\theta_2\cos(\phi_1-\phi_2)$$

What is the name of this formula?

• It looks an awful lot like the Spherical Law of Cosines.
– Blue
Jul 8, 2013 at 15:18
• This is the name I was looking for! Thanks, Blue!! Jul 12, 2013 at 1:35