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Calculus Level 3

W i t h o u t c a l c u l a t i o n , C a n y o u d e t e r m i n e w h i c h a r e a i s b i g g e r ? ? Without\quad calculation,\quad Can\quad you\quad determine\quad which\\ area\quad is\quad bigger\quad ??

A2 They're equal A1 The information isn't enough

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1 solution

Ahmad Hesham
Jul 15, 2015

U s i n g I n t e g r a t i o n t o g e t A 1 , A 2 A 1 = 0 1 2 x e x d x ( 1 ) A 2 = 0 1 e sin ( x ) sin ( 2 x ) d x sin ( 2 x ) = 2 sin ( x ) cos ( x ) A 2 = 0 1 2 e sin ( x ) sin ( x ) cos ( x ) d x L e t u = s i n ( x ) C h a n g e t h e b o u n d a r i e s i n t e r m s o f u x = 0 u = sin ( 0 ) = 0 x = 1 u = sin ( 1 ) d u = cos ( x ) d x A 2 = 0 sin ( 1 ) 2 u e u d u ( 2 ) F r o m ( 1 ) , ( 2 ) 0 1 2 x e x d x > 0 sin ( 1 ) 2 u e u d u A 1 > A 2 Using\quad Integration\quad to\quad get\quad { A }_{ 1 }\quad ,\quad { A }_{ 2 }\\ { A }_{ 1 }=\int _{ 0 }^{ 1 }{ 2x{ e }^{ x }dx } \quad \longrightarrow \quad (1)\\ { A }_{ 2 }=\int _{ 0 }^{ 1 }{ { e }^{ \sin { (x) } }\sin { (2x) } } dx\\ \because \quad \sin { (2x) } =2\sin { (x)\cos { (x) } } \\ \therefore { \quad A }_{ 2 }=\int _{ 0 }^{ 1 }{ 2 } { e }^{ \sin { (x) } }\sin { (x)\cos { (x) } } dx\\ Let\quad u=sin(x)\\ Change\quad the\quad boundaries\quad in\quad terms\quad of\quad u\\ x=0\quad \Longrightarrow \quad u=\sin { (0)=0 } \\ x=1\quad \Longrightarrow \quad u=\sin { (1) } \\ du=\cos { (x) } dx\\ \\ \therefore \quad { A }_{ 2 }=\int _{ 0 }^{ \sin { (1) } }{ 2u{ e }^{ u } } du\quad \longrightarrow \quad (2)\\ From\quad (1)\quad ,\quad (2)\\ \int _{ 0 }^{ 1 }{ 2x{ e }^{ x }dx } >\int _{ 0 }^{ \sin { (1) } }{ 2u{ e }^{ u } } du\\ \\ \boxed { \therefore { A }_{ 1 }{ \quad >\quad A }_{ 2 } }

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