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Calculus Level 4

0 1 C 7 207 x 200 ( 1 x ) 7 . d x \int _{ 0 }^{ 1 }{ { C }_{ 7 }^{ 207 } } x^{ 200 }{ (1-x) }^{ 7 }.dx

1 207 \frac { 1 }{ 207 } 1 208 \frac { 1 }{ 208 } 0 1

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2 solutions

Kartik Sharma
Jan 16, 2015

Use IBP repeatedly. Really liked this simple problem where just we have to do is to use IBP repeatedly and we get a nice result.

IBP is integration byparts but when used repeatedly it is not giving the answer would u please post it

Shagun Mehra - 5 years, 7 months ago

W e c a n a l s o s o l v e t h i s u s i n g p r o p e r t i e s o f B e t a a n d G a m m a f u n c t i o n s . B e t a f u n c t i o n i s d e f i n e d a s : B ( m , n ) = 0 1 x m 1 ( 1 x ) n 1 . d x T h e g i v e n i n t e g r a l c a n b e w r i t t e n a s C 7 207 . B ( 201 , 8 ) N o w u s i n g t h e p r o p e r t y B ( m , n ) = Γ m . Γ n Γ ( m + n ) w h e r e Γ n d e n o t e s t h e g a m m a f u n c t i o n . A n d u s i n g t h e p r o p e r t y Γ ( n + 1 ) = n . Γ ( n ) I t c a n b e f o u n d t h a t Γ ( 201 ) = 200 ! a n d Γ ( 8 ) = 7 ! A l s o Γ ( 209 ) = 208 ! a n d C 7 207 = 207 ! 200 ! 7 ! U s i n g t h e s e r e s u l t s w e g e t A n s w e r a s 1 208 . We\quad can\quad also\quad solve\quad this\quad using\quad properties\quad of\quad Beta\quad and\quad \\ Gamma\quad functions.\\ \\ Beta\quad function\quad is\quad defined\quad as\quad :\quad B(m,n)\quad =\quad \int _{ 0 }^{ 1 }{ { x }^{ m-1 }{ (1-x) }^{ n-1 } } .dx\\ \\ The\quad given\quad integral\quad can\quad be\quad written\quad as\quad { C }_{ 7 }^{ 207 }.B(201,8)\\ \\ Now\quad using\quad the\quad property\quad B(m,n)\quad =\quad \frac { \Gamma m.\Gamma n }{ \Gamma (m+n) } \quad where\quad \\ \Gamma n\quad denotes\quad the\quad gamma\quad function.\\ \\ And\quad using\quad the\quad property\quad \Gamma (n+1)\quad =\quad n.\Gamma (n)\\ \\ It\quad can\quad be\quad found\quad that\quad \Gamma (201)\quad =\quad 200!\quad and\quad \Gamma (8)\quad =\quad 7!\\ Also\quad \Gamma (209)\quad =\quad 208!\quad and\quad { C }_{ 7 }^{ 207 }\quad =\quad \frac { 207! }{ 200!7! } \\ Using\quad these\quad results\quad we\quad get\quad Answer\quad as\quad \boxed { \frac { 1 }{ 208 } } .\\

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