The minimum of two curves

Calculus Level 3

2 2 min { x x , x x } d x = ? \int _{-2}^{2} \min\big\{x-\lfloor x \rfloor,-x - \lfloor-x \rfloor\big\} \, dx = \, ?


The answer is 1.

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2 solutions

Deepanshu Gupta
Oct 28, 2014

Let this Integral be I I

now as shown in The graph By symmetry This Integral is equal to

I n e t e g r a l = 4 × A r e a s h a d e d t r i n g l e = 4 × ( 1 2 × 1 2 × 1 ) = 1 Inetegral\quad =\quad 4\quad \times \quad { Area }_{ shaded\quad tringle }\\ \quad \quad \quad \quad \quad \quad \quad \quad =\quad 4\quad \times \quad (\frac { 1 }{ 2 } \times \frac { 1 }{ 2 } \times 1)\\ \quad \quad \quad \quad \quad \quad \quad \quad =\quad 1\quad .

graph graph

I like graphs a lot !

Abhishek Singh - 6 years, 7 months ago

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I too love graphs. Just love 'em.

Aakarshit Uppal - 6 years, 4 months ago

same method

Figel Ilham - 6 years, 6 months ago
Sanjeet Raria
Oct 28, 2014

The integrand is

m i n { { x } , { x } } \large min\{\{x\},\{-x\}\}

Well if we analyze its graph between 0 0 to 1 1 , it will sort of like be an isosceles triangle with height = 1 2 =\frac{1}{2} & base equal to 1 1 unit. Since it's a periodic function, there will be a total of four such triangles in [ 2 , 2 ] [-2,2] .

Thus the required definite integral equal to the total area of these triangles which is obviously 4 ( 1 2 ) ( 1 2 ) = 1 4(\frac{1}{2}) (\frac{1}{2})=\boxed 1

Can someone tell me how can i put {x} in latex?? It shows x instead of {x}

Sanjeet Raria - 6 years, 7 months ago

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{ abc } \text{\{ abc \}} gives { a b c } \{abc\}

Samuraiwarm Tsunayoshi - 6 years, 7 months ago

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