One more thing, how will I get the derivative of cos2(theta)?

Question

hartnn · Answer

know the chain rule ?

abb0t · Answer

$$\cos^2(\theta)$$ correct? Follow what @hartnn said.

hartnn · Answer

i think its $\cos 2 \theta$

anonymous · Answer

no, it was actually cos2(theta)

abb0t · Answer

I think it might be more clear if you put the 2 inside the parenthesis, just for future reference, but either way, you would still use the chain rule.

hartnn · Answer

so do u know derivative of cos theta ?

anonymous · Answer

it's -sin theta

hartnn · Answer

so do u know how to use chain rule to get derivative of cos 2theta ?

hartnn · Answer

$f(g(x))' = f'(g(x))\times g'(x)$
so, $(\cos 2\theta )'=(-\sin 2\theta )\times (2\theta)'=....?$

anonymous · Answer

ahhh...it's basically the chain rule

anonymous · Answer

I though I would have to use some trig identity

hartnn · Answer

thats what i first asked :P 
so what u got ?

hartnn · Answer

if u got -2sin 2theta, then its correct

anonymous · Answer

thanks! I did :)