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Calculus Level 4

e 3 x + e x e 4 x e 2 x + 1 d x \large \int \dfrac{e^{3x} + e^x}{e^{4x} - e^{2x} + 1} \, dx

If the value of the indefinite integral above can be written as arctan ( a e b x g e d x ) + C , \arctan(ae^{bx} - ge^{dx} ) + C , where a , b , d a,b,d and g g are constant integers, find 101 ( a 2 + b + d 3 + g 4 ) 101(a^2+b + d^3 + g^4) .

Clarification : C C denotes the arbitrary constant of integration .


The answer is 202.

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3 solutions

Rishabh Jain
May 4, 2016

Divide numerator and denominator by e 2 x e^{2x} to write it as: ( e x + e x ) d x e 2 x 1 + e 2 x ( e x e x ) 2 + 1 \Large\displaystyle\int\dfrac{(e^x+e^{-x})\mathrm{d}x}{\underbrace{e^{2x}-1+e^{2x}}_{\Large\color{#D61F06}{(e^x-e^{-x})^2+1}}}

Substitute e x e x = t e^x-e^{-x}=t such that ( e x + e x ) d x = d t (e^x+e^{-x})\mathrm{d}x=\mathrm{d}t .

d t t 2 + 1 = tan 1 t + C \Large \displaystyle\int\dfrac{\mathrm{d}t}{t^2+1}=\tan^{-1}t+C

= tan 1 ( e x e x ) + C \Large =\tan^{-1}(e^x-e^{-x})+C

a = b = g = 1 , d = 1 \large \implies a=b=g=1, d=-1

101 ( a 2 + b + d 3 + g 4 ) = 202 \large \therefore 101(a^2+b+d^3+g^4)=\boxed{202}

Rahul Saxena
Jun 17, 2015

Lu Chee Ket
Feb 11, 2015

Nice Approach

But you should latixfy it .

Rajdeep Dhingra - 6 years, 4 months ago

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To learn it utilizing time.

Lu Chee Ket - 6 years, 4 months ago

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No need.

Just click here

Rajdeep Dhingra - 6 years, 4 months ago

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@Rajdeep Dhingra This looked very interesting to me. Thanks very much!

Lu Chee Ket - 6 years, 4 months ago

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@Lu Chee Ket Your Welcome. :)

Rajdeep Dhingra - 6 years, 4 months ago

@Lu Chee Ket See the image below.

Imgur Imgur Imgur Imgur Enclose Latex code in R o u n d b r a c k e t s Round brackets to display in the same line or in S q u a r e B r a c k e t s Square Brackets to display in other line.

Hover to see the latex code

Rajdeep Dhingra - 6 years, 4 months ago

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@Rajdeep Dhingra Please give comment on my very first paste.

Lu Chee Ket - 6 years, 4 months ago

Nicely done .

But i told you how to view latex without pasting images.

hover to see Latex codes.If want in continuation in the same line then like 0 3 x 3 d x \int_{0}^{3}{x^{3}dx} is fine. Or in different line use 0 3 x 3 d x \int_{0}^{3}{x^{3}dx} Imgur Imgur

Rajdeep Dhingra - 6 years, 4 months ago

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Your gradual guiding way looked good to me. I started to feel not that difficult to learn. Starting with some being known, I think we can learn all eventually. Thanks!

Lu Chee Ket - 6 years, 4 months ago

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Happy to help. :)

Rajdeep Dhingra - 6 years, 4 months ago

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