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Calculus Level 5

Evaluate

0 1 ( ( 1 x 2014 ) 1 2014 x ) 2 . d x ) {|\displaystyle \int_{0}^{1}((1-x^{2014})^{\frac{1}{2014}}-x)^{2}.dx)|}

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The answer is 0.33.

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2 solutions

Tanishq Varshney
Mar 19, 2015

I = 0 1 ( ( 1 x a ) 1 a x ) 2 . d x I=\displaystyle \int_{0}^{1} ((1-x^{a})^{\frac{1}{a}}-x)^{2}.dx

let x a = t x^{a}=t

a x a 1 d x = d t ax^{a-1}dx=dt

I = 1 a 0 1 ( ( 1 t ) 1 a t 1 a ) 2 t 1 a 1 d t I=\frac{1}{a} \displaystyle \int_{0}^{1}((1-t)^{\frac{1}{a}}-t^{\frac{1}{a}})^{2}~t^{\frac{1}{a}-1}dt

let 1 a = c \frac{1}{a}=c

I = c 0 1 ( ( 1 t ) c t c ) 2 t c 1 d t I=c \displaystyle \int_{0}^{1}((1-t)^{c}-t^{c})^{2}t^{c-1}dt ......... ( 1 ) (1)

using a b f ( x ) d x = a b f ( a + b x ) d x \displaystyle \int_{a}^{b}f(x)dx=\displaystyle \int_{a}^{b}f(a+b-x)dx

I = c 0 1 ( ( 1 t ) c t c ) 2 ( 1 t ) c 1 d t I=c \displaystyle \int_{0}^{1}((1-t)^{c}-t^{c})^{2}(1-t)^{c-1}dt ...... ( 2 ) (2)

adding 1 1 and 2 2

2 I = c 0 1 ( ( 1 t ) c t c ) 2 ( ( 1 t ) c 1 + t c 1 ) d t 2I=c \displaystyle \int_{0}^{1}((1-t)^{c}-t^{c})^{2}((1-t)^{c-1}+t^{c-1})dt

let ( 1 t ) c t c = z (1-t)^{c}-t^{c}=z

2 I = 1 1 z 2 d z 2I=-\displaystyle \int_{1}^{-1} z^{2}dz

2 I = 1 1 z 2 d z 2I= \displaystyle \int_{-1}^{1}z^{2}dz

2 I = 2 0 1 z 2 d z 2I=2 \displaystyle \int_{0}^{1}z^{2}dz

I = 1 3 I=\frac{1}{3}

indeed very nice

Kyle Finch - 6 years, 2 months ago

What is the property you used in line 7 or so called?

Ryan Tamburrino - 6 years, 2 months ago

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there are some basic definite integral properties and it is one of them.

Tanishq Varshney - 6 years, 2 months ago

@Tanishq Varshney Nice solution! +1

User 123 - 6 years, 1 month ago

@Tanishq Varshney Sorry, but I had a doubt. Please could you help me? I = c 0 1 ( ( 1 t ) c t c ) 2 t c 1 d t I=c \displaystyle \int_{0}^{1}((1-t)^{c}-t^{c})^{2}t^{c-1}dt ......... ( 1 ) (1) using a b f ( x ) d x = a b f ( a + b x ) d x \displaystyle \int_{a}^{b}f(x)dx=\displaystyle \int_{a}^{b}f(a+b-x)dx I = c 0 1 ( ( 1 t ) c t c ) 2 ( 1 t ) c 1 d t I=c \displaystyle \int_{0}^{1}((1-t)^{c}-t^{c})^{2}(1-t)^{c-1}dt ...... ( 2 ) (2) adding 1 1 and 2 2 In ( 2 ) (2) , what did you take as f ( t ) f(t) ? I noticed that you rewrote the second bracket as ( 1 + 0 t ) c 1 (1+0-t)^{c-1} . But why did you change nothing in the first bracket: ( ( 1 t ) c t c ) 2 ((1-t)^{c}-t^{c})^{2} ? Shouldn't the same rule be applied here also?

User 123 - 6 years, 1 month ago

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Becoz it comes out to be the same, and as whole square is there , no need to check of minus sign. hope it helps

Tanishq Varshney - 6 years, 1 month ago

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Just noticed it, thanks very much!

User 123 - 6 years, 1 month ago

Could you please post a solution to A Tricky Integral for some ? Many thanks in advance! @Tanishq Varshney

User 123 - 6 years, 1 month ago

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@Tanishq Varshney Apologies for giving you this trouble...

User 123 - 6 years, 1 month ago
Vishwas Gajera
Mar 19, 2015

X is in (0 1),so x^2014=0

a good approximation, that could be also done. Thats why i generalised the integral

Tanishq Varshney - 6 years, 2 months ago

Same :) , Our Good Luck !

Deepanshu Gupta - 6 years, 2 months ago

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