The answer is where all Math begins

Calculus Level 4

33 1 4 41 1 4 32 7 ( x 3 + x 4 ) + 8 x 2 ( 31 17 7 ) + 6 x ( 31 12 7 ) + 31 + 164 7 2 ( 1 + 2 x ) ( 41 18 x 34 x 2 + 8 ( x 3 + x 4 ) ) d x = A π B + C ln ( D + 1 E + 1 ) \int _{ \frac {\sqrt { 33 } -1}4}^{\frac {\sqrt { 41 } -1}4} \frac {32\sqrt 7( x^3 +x^4) +8x^2 ( \sqrt { 31 } -17\sqrt 7) +6x (\sqrt { 31 } -12\sqrt 7) +\sqrt { 31 } +164\sqrt 7}{2 (1+2x)\left(41-18x-34x^2+8( x^3+x^4)\right)} dx = \frac { \sqrt A \pi}B +\sqrt C \ln \left( \frac { \sqrt D +1}{ \sqrt E +1} \right)

Positive integers A A , B B , C C , D D , and E E , where gcd ( A , B ) = gcd ( B , C ) = gcd ( C , D ) = gcd ( D , E ) = 1 \gcd(A,B)=\gcd(B,C)=\gcd(C,D)=\gcd(D,E)=1 , satisfy the equation above. Find A 8 B C D + E \dfrac {A-8B}{C-D+E} .


The answer is 1.

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1 solution

Rutwik Pasani
Mar 4, 2018

T h e i n t e g r a n d c a n b e s i m p l i f i e d a s f o l l o w s ( 32 7 ( x 3 + x 4 ) + 8 x 2 ( 31 17 7 ) + 6 x ( 31 12 7 ) + 31 + 164 7 ) 2 ( 1 + 2 x ) ( 41 18 x 34 x 2 + 8 ( x 3 + x 4 ) ) ( 32 7 x 3 + 32 7 x 4 136 7 x 2 72 7 x + 164 7 ) 32 x 5 + 48 x 4 120 x 3 140 x 2 + 128 x + 82 + ( 8 31 x 2 + 6 31 x + 31 ) 32 x 5 + 48 x 4 120 x 3 140 x 2 + 128 x + 82 7 ( 32 x 3 + 32 x 4 136 x 2 72 x + 164 ) 32 x 5 + 48 x 4 120 x 3 140 x 2 + 128 x + 82 + 31 ( 8 x 2 + 6 x + 1 ) 32 x 5 + 48 x 4 120 x 3 140 x 2 + 128 x + 82 W h i c h a f t e r a t e d i o u s l o n g d i v i s o n s i m p l i f i e s t o 2 7 ( 2 x + 1 ) + 31 ( 4 x + 1 ) 16 x 4 + 16 x 3 68 x 2 36 x + 82 T h e r e f o r e t h e p r o b l e m s i m p l i f i e s t o 2 7 ( 2 x + 1 ) + 31 ( 4 x + 1 ) 16 x 4 + 16 x 3 68 x 2 36 x + 82 d x 2 7 ( 2 x + 1 ) d x + 31 ( 4 x + 1 ) 16 x 4 + 16 x 3 68 x 2 36 x + 82 d x T h e f i r s t i n t e g r a l i s t h e d e r i v a t i v e o f 7 ln ( 2 x + 1 ) a n d t h e s e c o n d i n t e g r a l f u r t h e r s i m p l i f i e s a s f o l l o w s . . 31 ( 4 x + 1 ) 16 x 4 + 16 x 3 68 x 2 36 x + 82 d x 31 2 2 ( 4 x + 1 ) ( 16 x 4 + 16 x 3 68 x 2 36 x + 81 ) + 1 d x 31 2 ( 8 x + 2 ) 1 + ( 4 x 2 + 2 x 9 ) 2 d x T h i s i s j u s t t h e d e r i v a t i v e o f 31 2 arctan ( 4 x 2 + 2 x 9 ) T h e r e f o r e t h e i n t e g r a l f i n a l l y i s [ 7 ln ( 2 x + 1 ) + 31 2 arctan ( 4 x 2 + 2 x 9 ) ] w h i c h o n p u t t i n g p r o p e r l i m i t s a n d e v a l u a t i n g e q u a l s 31 π 4 + 7 ln ( ( 41 + 1 ) 33 + 1 ) A = 31 B = 4 C = 7 D = 41 E = 33 A n d t h u s , ( A 8 B ) C D + E = 1 The\quad integrand\quad can\quad be\quad simplified\quad as\quad follows-\\ \Rightarrow \frac { \left( 32\sqrt { 7 } \left( x^{ 3 }+x^{ 4 } \right) +8x^{ 2 }\left( \sqrt { 31 } -17\sqrt { 7 } \right) +6x\left( \sqrt { 31 } -12\sqrt { 7 } \right) +\sqrt { 31 } +164\sqrt { 7 } \right) }{ 2\left( 1+2x \right) \left( 41-18x-34x^{ 2 }+8\left( x^{ 3 }+x^{ 4 } \right) \right) } \\ \\ \Rightarrow \frac { \left( 32\sqrt { 7 } x^{ 3 }+32\sqrt { 7 } x^{ 4 }-136\sqrt { 7 } x^{ 2 }-72\sqrt { 7 } x+164\sqrt { 7 } \right) }{ 32x^{ 5 }+48x^{ 4 }-120x^{ 3 }-140x^{ 2 }+128x+82 } +\frac { \left( 8\sqrt { 31 } x^{ 2 }+6\sqrt { 31 } x+\sqrt { 31 } \right) }{ 32x^{ 5 }+48x^{ 4 }-120x^{ 3 }-140x^{ 2 }+128x+82 } \\ \\ \Rightarrow \sqrt { 7 } \frac { \left( 32x^{ 3 }+32x^{ 4 }-136x^{ 2 }-72x+164 \right) }{ 32x^{ 5 }+48x^{ 4 }-120x^{ 3 }-140x^{ 2 }+128x+82 } +\sqrt { 31 } \frac { \left( 8x^{ 2 }+6x+1 \right) }{ 32x^{ 5 }+48x^{ 4 }-120x^{ 3 }-140x^{ 2 }+128x+82 } \\ \\ Which\quad after\quad a\quad tedious\quad long\quad divison\quad simplifies\quad to-\\ \Rightarrow \frac { 2\sqrt { 7 } }{ \left( 2x+1 \right) } +\frac { \sqrt { 31 } \left( 4x+1 \right) }{ 16x^{ 4 }+16x^{ 3 }-68x^{ 2 }-36x+82 } \\ \\ Therefore\quad the\quad problem\quad simplifies\quad to-\\ \\ \Rightarrow \int { \frac { 2\sqrt { 7 } }{ \left( 2x+1 \right) } +\frac { \sqrt { 31 } \left( 4x+1 \right) }{ 16x^{ 4 }+16x^{ 3 }-68x^{ 2 }-36x+82 } } dx\\ \\ \Rightarrow \int { \frac { 2\sqrt { 7 } }{ \left( 2x+1 \right) } } dx\quad +\int { \frac { \sqrt { 31 } \left( 4x+1 \right) }{ 16x^{ 4 }+16x^{ 3 }-68x^{ 2 }-36x+82 } } dx\\ The\quad first\quad integral\quad is\quad the\quad derivative\quad of\quad \sqrt { 7 } \ln { (2x+1) } \quad and\quad the\quad second\quad integral\quad further\quad simplifies\quad as\quad follows..\\ \\ \Rightarrow \int { \frac { \sqrt { 31 } \left( 4x+1 \right) }{ 16x^{ 4 }+16x^{ 3 }-68x^{ 2 }-36x+82 } } dx\quad \\ \Rightarrow \frac { \sqrt { 31 } }{ 2 } \int { \frac { 2\left( 4x+1 \right) }{ (16x^{ 4 }+16x^{ 3 }-68x^{ 2 }-36x+81)+1 } } dx\\ \Rightarrow \frac { \sqrt { 31 } }{ 2 } \int { \frac { \left( 8x+2 \right) }{ 1+\left( 4x^{ 2 }+2x-9 \right) ^{ 2 } } } dx\\ This\quad is\quad just\quad the\quad derivative\quad of\quad \frac { \sqrt { 31 } }{ 2 } \arctan { (4x^{ 2 }+2x-9) } \\ \\ Therefore\quad the\quad integral\quad finally\quad is\quad \left[ \sqrt { 7 } \ln { (2x+1) } \quad +\quad \frac { \sqrt { 31 } }{ 2 } \arctan { (4x^{ 2 }+2x-9) } \right] \quad which\quad on\quad putting\quad proper\quad limits\quad and\quad evaluating\quad equals-\\ \frac { \sqrt { 31 } \pi }{ 4 } +\sqrt { 7 } \ln { \left( \frac { \left( \sqrt { 41 } +1 \right) }{ \sqrt { 33 } +1 } \right) } \\ \therefore \boxed { A=31\\ B=4\\ C=7\\ D=41\\ E=33 } \quad And\quad thus,\quad \boxed { \quad \frac { (A-8B) }{ C-D+E } =1\quad } \\ \\ \\

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