Calcul-(us)-ator

Calculus Level 4

lim x 0 e x sin x x x 2 x 2 + x log e ( 1 x ) + lim x 0 2 sin x + 1 2 log e 1 + x 1 x 3 x x 5 \lim_{x\to0 } \dfrac{ e^x \sin x - x - x^2}{x^2 + x \log_e(1-x) } + \lim_{x\to0} \dfrac{2\sin x + \frac12 \log_e\frac{1+x}{1-x} - 3x}{x^5}

Evaluate the limit above to 2 decimal places.


The answer is -0.45.

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1 solution

Ayon Ghosh
Mar 12, 2017

This is my solution.Yours may be different.

Firstly,we recall and use some T r i g o n o m e t r i c a l Trigonometrical and L o g a r i t h m i c Logarithmic Series namely e x e^x = = 1 1 + + x x + + x 2 2 ! \frac{x^2}{2!} + + x 3 3 ! \frac{x^3}{3!} + + ... , then we have s i n sin x x = = x x - x 3 3 ! \frac{x^3}{3!} + + x 5 5 ! \frac{x^5}{5!} - ...( x x is in r a d i a n s radians ) , then l o g e ( 1 x ) log_e(1-x) = = - x x - x 2 / 2 x^2/2 - x 3 / 3 x^3/3 - ...

For the second limit we have s i n sin x x which has been already mentioned, 1 2 \frac{1}{2} l o g e log_e 1 + x 1 x \frac{1+x}{1-x} = = x x + + x 3 3 \frac{x^3}{3} + + x 5 5 \frac{x^5}{5} + + ...

Finally using these special series on evaluating the limits separately (both limits are undetermined of the form 0 / 0 0/0 ) by cancelling x x and applying x x = = 0 0 after cancelling we arrive at 13 60 \frac{13}{60} + + 2 3 \frac{-2}{3} = = 0.45 -0.45 .

Edit: 4/7/17 hey now i now another solution we could simply differentiate both limits (L Hopital 's rules since it is of 0/0 form that 's easier instead of remembering all those taylor series.It's far easier to use this approach.

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