Originally Posted by

**evanator** Hi all,

I have a mental block on a certain very simple trigonometry problem. I know I will slap my forehead when I see the solution. I therefore ask for your indulgence and thank, in advance, any responders. Here is the question and my attempt:

Using $\displaystyle \tan \theta \equiv \frac{\sin \theta}{\cos \theta}$, show that the equation $\displaystyle \tan \theta = \sin \theta$ can be written as $\displaystyle \sin \theta (\cos \theta - 1) = 0$ provided that $\displaystyle \cos \theta \neq 0$.

Here is what I have done already:

$\displaystyle \tan \theta = \sin \theta$

$\displaystyle \sin \theta = \frac{\sin \theta}{\cos \theta}$

$\displaystyle \sin \theta = \sin \theta \cos \theta$

starting from the above step ...