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Q.If f(x)=log⁡(tan⁡ex)f(x) = \log(\tan e^{x}), then find f′(x)f'(x).

Telangana TsbieTelangana Board of Intermediate Education (Intermediate 1st Year) 2019Subjective· 2mImportance★★★★★
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Differentiate using the chain rule: derivative of log⁡(tan⁡u)\log(\tan u) is sec⁡2u⋅u′/tan⁡u\sec^2u \cdot u'/\tan u, with u=exu=e^x.

Given f(x)=log⁡(tan⁡ex)f(x) = \log(\tan e^{x}).

Let u=tan⁡(ex)u = \tan(e^{x}), so f(x)=log⁡uf(x) = \log u.

f′(x)=1u⋅dudxf'(x) = \frac{1}{u}\cdot\frac{du}{dx}

Now find dudx\dfrac{du}{dx} where u=tan⁡(ex)u=\tan(e^x):

dudx=sec⁡2(ex)⋅ddx(ex)=exsec⁡2(ex)\frac{du}{dx} = \sec^{2}(e^{x})\cdot \frac{d}{dx}(e^{x}) = e^{x}\sec^{2}(e^{x})

Therefore:

f′(x)=exsec⁡2(ex)tan⁡(ex)f'(x) = \frac{e^{x}\sec^{2}(e^{x})}{\tan(e^{x})}

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