Seems so complex !

Calculus Level 4

lim x 0 tan x 3 ln ( 1 + 3 x ) ( arctan x ) 2 ( e 5 × x 3 1 ) \lim_{x \to 0} {\frac{\tan \sqrt[3]{x} \ln(1+3x)}{(\arctan\sqrt{x})^{2}(e^{5 \times \sqrt[3]{x}}-1)}} where ln \ln stands for Logarithm with base e e

try more here


The answer is 0.6.

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3 solutions

Aritra Jana
Dec 1, 2014

i did this sum obviously ignoring the typo of 1 + 3 n 1+3n instead of 1 + 3 x 1+3x


We have a horrendous looking expression to ourselves.. but this is going to be solved by making it more horrendous looking:

our expression:

lim x 0 t a n x 3 . l n ( 1 + 3 x ) ( t a n 1 x ) 2 . ( e 5 x 3 1 ) \large{\lim\limits_{x\to 0}\dfrac{tan\sqrt[3]{x}.ln(1+3x)}{(tan^{-1}\sqrt{x})^{2}.(e^{5\sqrt[3]{x}}-1)}} ........... ( i ) (i)

we take: t a n 1 x = z x = t a n 2 z tan^{-1}\sqrt{x}=z \implies x=tan^{2}z

so that: x 0 z 0 x\to 0 \implies z\to 0

we also write: l n ( 1 + 3 x ) ( t a n 1 x ) 2 = l n ( 1 + 3. t a n 2 z ) 3. t a n 2 z . t a n 2 z z 2 . 3 \large{\dfrac{ln(1+3x)}{(tan^{-1}\sqrt{x})^{2}}=\dfrac{ln(1+3.tan^{2}z)}{3.tan^{2}z}.\dfrac{tan^{2}z}{z^{2}}.3}

now we write the horrendous expression into another more horrible looking (but beautiful) expression:

lim x 0 1 5 . ( t a n x 3 x 3 ) . ( 1 e 5 x 3 1 5 x 3 ) . ( l n ( 1 + 3. t a n 2 z ) 3. t a n 2 z ) . ( t a n 2 z z 2 ) . 3 \large{\lim\limits_{x\to 0}\frac{1}{5}.(\dfrac{tan\sqrt[3]{x}}{\sqrt[3]x}).(\dfrac{1}{\frac{e^{5\sqrt[3]{x}}-1}{5\sqrt[3]{x}}}).(\dfrac{ln(1+3.tan^{2}z)}{3.tan^{2}z}).(\dfrac{tan^{2}z}{z^{2}}).3}

Note that. applying limits in each of the brackets, we get 1 1

so, our end result: 1 5 . 1.1.1.1.3 = 3 5 = 0.6 \large{\frac{1}{5}.1.1.1.1.3=\frac{3}{5}=\boxed{0.6}}


@Abhishek Singh what do you think? :D

Gautam Sachdeva
Jun 4, 2017

(1+3n)===》》(1+3x)

Usama Khidir
May 29, 2015

Please do correct the term inside ln(1+3n) to ln(1+3x)

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