Inspiration is in the air

Calculus Level 5

0 x + 1 ( 1 ) x 2016 { x } d x 2 x = ? \large \displaystyle \int_{0}^\infty\lfloor x+1\rfloor\dfrac{(-1)^{\lfloor x\rfloor}\cdot 2016\cdot { \{x\} }\cdot dx}{2^{\lceil x\rceil}} = \, ?

Notations :


Inspiration .


The answer is 224.

This section requires Javascript.
You are seeing this because something didn't load right. We suggest you, (a) try refreshing the page, (b) enabling javascript if it is disabled on your browser and, finally, (c) loading the non-javascript version of this page . We're sorry about the hassle.

1 solution

Harsh Khatri
Apr 7, 2016

This problem is similar to this

Using a similar approach, we conclude that the given integral reduces to:

( r = 0 ( 1 ) r ( r + 1 ) 2 r + 1 ) 2016 1 2 \bigg( \displaystyle \sum_{r=0}^{\infty} \frac{(-1)^{r} \cdot (r+1)}{2^{r+1}} \bigg) \cdot 2016 \cdot \frac{1}{2}

504 ( r = 0 ( 1 2 ) r ( r + 1 ) ) \displaystyle \Rightarrow 504 \cdot \bigg( \displaystyle \sum_{r=0}^{\infty} \big(\frac{-1}{2}\big)^{r} \cdot (r+1) \bigg)

Let S = r = 0 ( 1 2 ) r ( r + 1 ) S = \displaystyle \sum_{r=0} \big( \frac{-1}{2} \big)^{r} \cdot (r+1)

S = 1 + ( 1 ) ( 2 ) 2 + ( 1 ) ( 3 ) 2 2 + \displaystyle \Rightarrow S = 1 + \frac{(-1)(2)}{2} + \frac{(1)(3)}{2^2} + \ldots

2 S = 2 + 2 + ( 1 ) ( 3 ) 2 + ( 1 ) ( 4 ) 2 2 + \displaystyle \Rightarrow -2S = - 2 + 2 + \frac{(-1)(3)}{2} + \frac{(1)(4)}{2^2} + \ldots

S ( 2 S ) = ( 1 0 ) + ( ( 1 ) ( 2 ) 2 ( 1 ) ( 3 ) 2 ) + ( ( 1 ) ( 3 ) 2 2 ( 1 ) ( 4 ) 2 2 ) + S-(-2S) = (1-0) + \big( \frac{(-1)(2)}{2} - \frac{(-1)(3)}{2} \big) + \big( \frac{(1)(3)}{2^2} - \frac{(1)(4)}{2^2} \big) + \ldots

3 S = 1 + 1 2 + 1 4 + \displaystyle \Rightarrow 3S = 1 + \frac{1}{2} + \frac{-1}{4} + \ldots

3 S = 1 + 1 2 1 1 2 \displaystyle \Rightarrow 3S = 1 + \frac{\frac{1}{2}}{1-\frac{-1}{2}}

S = 4 9 \displaystyle \Rightarrow S = \frac{4}{9}

Hence, the given integral now reduces to:

504 4 9 = 224 504 \cdot \frac{4}{9} = \boxed{224}

Thanks... (+1)..... I have included the link in the question itself..... If these problem gets some solvers I would surely post the father version ( Including Fibonnaci and some more functions)... BTW Nice.. :-)

Rishabh Jain - 5 years, 2 months ago

Log in to reply

Yeah, please do post those problems too.

Harsh Khatri - 5 years, 2 months ago

fabulous solution bro +1

Mardokay Mosazghi - 5 years, 2 months ago

Log in to reply

Thank you!

Harsh Khatri - 5 years, 2 months ago

0 pending reports

×

Problem Loading...

Note Loading...

Set Loading...