300 followers problem

Calculus Level 5

Let f ( x ) = max { x 2 , ( 1 x ) 2 , 2 x ( 1 x ) } { f(x) = \text{max}\left\{ { x }^{ 2 },{ \left( 1-x \right) }^{ 2 },2x(1-x) \right\} } .

Determine the area of the region bounded bt the curves y = f ( x ) y=f(x) , x x -axis, x = 0 , x = 1 x=0, x=1 .

If the area is of the form a b \frac a b for coprime positive integers a , b a,b , find a + b a+b .


This is a problem of my set JEE Calculus .


The answer is 44.

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1 solution

W e h a v e , f ( x ) = m a x { x 2 , ( 1 x ) 2 , 2 x ( 1 x ) } We \ have, \ f(x)\quad =\quad max\left\{ { x }^{ 2 },{ \left( 1-x \right) }^{ 2 },2x(1-x) \right\}

Considering only the above max region. So, f(x) can be written as,

f ( x ) = { ( 1 x ) 2 , f o r 0 x 1 3 2 x ( 1 x ) , f o r 1 3 x 2 3 x 2 , f o r 2 3 x 1 } f(x)=\left\{ \begin{matrix} { (1-x) }^{ 2 }\quad ,\quad \quad \quad for\quad 0\le x\le \frac { 1 }{ 3 } \\ 2x(1-x)\quad ,\quad \quad \quad for\quad \frac { 1 }{ 3 } \le x\le \frac { 2 }{ 3 } \\ { x }^{ 2 }\quad ,\quad \quad \quad \quad \quad for\quad \frac { 2 }{ 3 } \le x\le 1 \end{matrix} \right\}

A r e a B o u n d e d = 0 1 3 ( 1 x ) 2 d x + 1 3 2 3 2 x ( 1 x ) d x + 2 3 1 ( x 2 ) d x \therefore \ Area\ Bounded =\int _{ 0 }^{ \frac { 1 }{ 3 } }{ { \left( 1-x \right) }^{ 2 } } dx \ +\int _{ \frac { 1 }{ 3 } }^{ \frac { 2 }{ 3 } }{ 2x(1-x) } dx \ +\int _{ \frac { 2 }{ 3 } }^{ 1 }{ \left( { x }^{ 2 } \right) } dx

= 17 27 s q . u n i t s = \large{\boxed{\frac{17}{27} sq. \ units}}

a + b = 44 \therefore \quad \quad \quad a\quad +\quad b\quad =\quad \boxed{44}

a bit calculative and tedious, i got 325 points for this ¨ \ddot \smile

Tanishq Varshney - 6 years, 1 month ago

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So did I . I'm Happy ! ;)

Keshav Tiwari - 6 years, 1 month ago

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