Ecstacy of 'e'............

Calculus Level 4

Evaluate

lim x 0 ( 1 + tan x ) cot x e + e tan x 2 tan 2 x . \lim_{x\rightarrow0}\frac{(1+\tan x)^{\cot x}-e+\frac{e\tan x}{2}}{\tan^2x}.


The answer is 1.245.

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1 solution

Jatin Yadav
Mar 26, 2014

The dots would mean unnecessary higher powers.

( 1 + tan x ) cot x = e ln ( 1 + tan x ) tan x = e 1 tan x 2 + tan 2 x 3 + \displaystyle (1+ \tan x)^{\cot x} = e^{\frac{\ln(1+\tan x)}{\tan x}} = e^{1 - \frac{\tan x}{2} + \frac{\tan^2 x}{3} + \dots}

= e ( e tan x 2 + tan 2 x 3 + ) \displaystyle e \bigg(e^{\frac{-\tan x}{2} + \frac{\tan^2 x}{3} + \dots} \bigg)

= e ( 1 tan x 2 + t a n 2 x 3 + 1 2 ( tan x 2 + t a n 2 x 3 ) 2 + ) \displaystyle e \bigg(1 -\frac{\tan x}{2} + \frac{tan^2 x}{3} \dots + \frac{1}{2} \big(-\frac{\tan x}{2} + \frac{tan^2 x}{3} \dots\big)^2 + \dots\bigg)

= e ( 1 tan x 2 + tan 2 x 3 + tan 2 x 8 + ) \displaystyle e\bigg( 1 - \frac{\tan x}{2} + \frac{\tan^2 x}{3} + \frac{\tan^2 x}{8 } + \dots\bigg)

= e ( 1 t a n x 2 + 11 24 tan 2 x + ) \displaystyle e \bigg(1 - \frac{tan x}{2} + \frac{11}{24} \tan^2 x + \dots\bigg)

Hence, the numerator of the asked expression becomes e ( 11 24 tan 2 x + ) e\bigg(\frac{11}{24} \tan^2 x + \dots \bigg)

Hence, the answer is 11 e 24 \boxed{\frac{11e}{24}}

Awesome man. You truly nailed it! Thats how I expected it to be solved.

Satyam Bhardwaj - 7 years, 2 months ago

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