Find any critical numbers of: f(theta) = 2sec(theta) + tan(theta), 0<theta<2pi.

I found the defivative, but I got stuck.

I got to 2tan(theta)=-sin(theta).

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- Oct 31st 2007, 09:57 PMunluckykcFind Critical numbers
Find any critical numbers of: f(theta) = 2sec(theta) + tan(theta), 0<theta<2pi.

I found the defivative, but I got stuck.

I got to 2tan(theta)=-sin(theta). - Oct 31st 2007, 09:59 PMJhevon
- Oct 31st 2007, 10:08 PMunluckykc
Oh, sorry. I got to include the steps.

f'(theta) = 2sec(theta)tan(theta) + sec^2(theta)

I set it equal to zero, factored out a sec(theta). I was left with 2 equations: sec(theta)=0 and 2tan(theta) + sec(theta) = 0 =>2tan(theta) = -sec(theta) {I didn't mean sin before...I meant sec} - Oct 31st 2007, 10:14 PMJhevon
ok. and you are aware that $\displaystyle \sec \theta $ is never zero, correct?

anyway, here's how i would proceed.

$\displaystyle 2 \tan \theta + \sec \theta = 0$

$\displaystyle \Rightarrow \frac {2 \sin \theta }{\cos \theta} + \frac 1{\cos \theta } = 0$

now combine the fractions and set the numerator equal to zero and solve for theta