Originally Posted by JennyFlowers
Sorry, what I meant was that the last step in post #3 was:

$\frac{\sin (x)}{1- \cos (x)}$

I'm not sure how that is the same as where you're starting from:

$\frac{1}{1 - \cos (x)}$
Do you not see how you would replace $\frac{1}{1 - \cos (x)}$ in your line with the expression for it that I gave you? I can understand it might be hard to see by yourself, but given that I have pointed it out - three times now - do you not see that you multiply the numerator and denominator of your expression with $\frac{1 + \cos(x)}{1 + \cos (x)}$ ....?