confused about derivatives

wendywoo · Oct 23, 2011

i got this wrong on my quiz. the question is find dr/dƟ if r = (secƟ)(tan2Ɵ)

my answer is (sec Ɵ)(2tan Ɵsec Ɵ)(2)+(tan2 Ɵ)(sec Ɵtan Ɵ)

i dont understand how that is wrong http://en.wikipedia.org/wiki/Ɵ. the question is to take the derivative of r yes? i used the power rule and the chain rule. can someone show me what steps i missed?

tkhunny · Oct 23, 2011

wendywoo said:
(2tan Ɵsec Ɵ)(2)

No good.

1) It should still be \(\displaystyle 2\theta\).

2) \(\displaystyle \frac{d}{d\theta}tan(\theta) = sec^{2}(\theta)\)