# Homework Help: Dervative of trig functions.

1. Nov 28, 2009

### cheezeitz

1. The problem statement, all variables and given/known data

y' = csc2($$\vartheta$$ / 2 )
Find y"

3. The attempt at a solution

So far, i have 2 csc ($$\vartheta$$/2) *csc($$\vartheta$$/2)cot($$\vartheta$$/2) * 1/2

but i'm wondering, how do you take the derivative of a half angle identity?
or does it just simplify down to csc2($$\vartheta$$ / 2) * cot($$\vartheta$$/2)

2. Nov 28, 2009

### xeno_gear

You don't need to worry about derivatives of half-angle identities here. You're right about how it simplifies, and you used the chain rule properly, except you're missing a minus sign (the derivative of csc(x) is -csc(x)cot(x)).