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Calculus Level 5

0 1 log ( x ) ( log ( 1 x ) ) 3 x d x = A ζ ( 2 B + 1 ) π c D ζ ( 2 E + 1 ) \int _{ 0 }^{ 1 }{ \frac { \log { \left( x \right) { \left( \log { \left( 1-x \right) } \right) }^{ 3 } } }{ x } dx } =A\zeta \left( 2B+1 \right) -\frac { { \pi }^{ c } }{ D } \zeta \left( 2E+1 \right)

A , B , C , D , E A,B,C,D,E are positive integers. Find A + B + C + D + E A+B+C+D+E .


The answer is 18.

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2 solutions

Mark Hennings
Feb 26, 2016

We have 0 1 ln x ln 3 ( 1 x ) x d x = 0 1 ln ( 1 x ) ln 3 x 1 x d x = n = 1 H n 0 1 x n ln 3 x d x = 6 n = 1 H n ( n + 1 ) 4 = 6 n = 1 ( H n + 1 ( n + 1 ) 4 1 ( n + 1 ) 5 ) = 6 n = 2 ( H n n 4 1 n 5 ) = 6 n = 1 ( H n n 4 1 n 5 ) = 6 [ 3 ζ ( 5 ) 1 6 π 2 ζ ( 3 ) ζ ( 5 ) ] = 12 ζ ( 5 ) π 2 ζ ( 3 ) \begin{array}{rcl} \displaystyle \int_0^1 \frac{\ln x \ln^3(1-x)}{x}\,dx & = & \displaystyle \int_0^1 \frac{\ln(1-x) \ln^3x}{1-x}\,dx \\ & = & \displaystyle -\sum_{n=1}^\infty H_n \int_0^1 x^n \ln^3x\,dx \\ & = & \displaystyle 6\sum_{n=1}^\infty \frac{H_n}{(n+1)^4} \\ & = & \displaystyle 6\sum_{n=1}^\infty \left(\frac{H_{n+1}}{(n+1)^4} - \frac{1}{(n+1)^5}\right) \\ & = & \displaystyle 6\sum_{n=2}^\infty \left( \frac{H_n}{n^4} - \frac{1}{n^5}\right) \\ & = & \displaystyle 6\sum_{n=1}^\infty \left( \frac{H_n}{n^4} - \frac{1}{n^5}\right) \\ & = & \displaystyle 6\left[ 3\zeta(5) - \tfrac16\pi^2\zeta(3) - \zeta(5)\right] \\ & = & \displaystyle 12\zeta(5) - \pi^2\zeta(3) \end{array} making the answer 12 + 2 + 2 + 1 + 1 = 18 12 + 2 + 2 + 1 + 1 = \boxed{18} .

Sir is there a way I can contact you personally?

Aditya Kumar - 5 years, 3 months ago
Ishan Singh
Feb 26, 2016

Aliter :

0 1 log ( x ) ( log ( 1 x ) ) 3 x d x = lim a 0 + lim b 1 ( a ( 3 b 3 B ( a , b ) ) ) \displaystyle \int _{ 0 }^{ 1 }{ \dfrac { \log { \left( x \right) { \left( \log { \left( 1-x \right) } \right) }^{ 3 } } }{ x } \mathrm{d}x } = \lim_{a \to 0^+} \lim_{b \to 1} \left(\dfrac{\partial}{\partial a} \left(\dfrac{\partial^3}{\partial b^3} \operatorname{B} (a,b)\right) \right)

= 12 ζ ( 5 ) π 2 ζ ( 3 ) = 12\zeta(5) - \pi^2\zeta(3)

A + B + C + D + E = 18 \implies A+B+C+D+E = \boxed{18}

How do you write this ?????

Rishabh Deep Singh - 5 years, 3 months ago

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