1. ## Derive tan (x/2)

The question is: Show that $(tan(x/2))' = 1/(1+cos(x))$.

$tan(x/2)' = 1/(2(cos (x/2)^2)$, but I have no idea where to go from here.

2. cos(x/2)=sqrt((1+cosx)/2)

3. Originally Posted by chickenslowfood
The question is: Show that $(tan(x/2))' = 1/(1+cos(x))$.

$tan(x/2)' = 1/(2(cos (x/2)^2)$, but I have no idea where to go from here.
You need to know about half angle formula. Look at this:

List of trigonometric identities - Wikipedia, the free encyclopedia

4. ## Solved it now

Thanks for the help. I bet those half-angle and double-angle formulas might be useful.