Floor on the floor ??

Calculus Level 5

Evaluate 1 1 1008 + x x 2014 + 1 d x \int_{-1}^{1} \Bigg \lfloor 1008 + \dfrac{ \lfloor x \rfloor }{x^{2014} + 1} \Bigg \rfloor dx


The answer is 2015.

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1 solution

We could break up the limits of the integral, and hence instead of 1 1 \int_{-1}^{1} it can be 1 0 \int_{-1}^{0} and 0 1 \int_{0}^{1}

The function 1008 + x x 2014 + 1 \Bigg \lfloor 1008 + \dfrac{ \lfloor x \rfloor}{x^{2014} + 1}\Bigg \rfloor is

1008 + 1 x 2014 + 1 \Bigg \lfloor 1008 + \dfrac {-1}{x^{2014} + 1} \Bigg \rfloor for x in the interval ( 1 , 0 ) (-1,0)

Since x belongs to ( 1 , 0 ) (-1,0) , 1 x 2014 + 1 \dfrac{-1}{x^{2014} + 1} is a small negative quantity.

Hence

1008 + 1 x 2014 + 1 \Bigg \lfloor 1008 + \dfrac {-1}{x^{2014} + 1} \Bigg \rfloor for x in the interval ( 1 , 0 ) (-1,0) is equal to 1007 \boxed{1007}

and

1008 + 0 x 2014 + 1 \Bigg \lfloor 1008 + \dfrac {0}{x^{2014} + 1} \Bigg \rfloor for x in the interval ( 0 , 1 ) (0,1)

Since x belongs to ( 0 , 1 ) (0,1) , 1 x 2014 + 1 \dfrac{1}{x^{2014} + 1} is a small positive quantity.

Hence

1008 + 1 x 2014 + 1 \Bigg \lfloor 1008 + \dfrac {-1}{x^{2014} + 1} \Bigg \rfloor for x in the interval ( 0 , 1 ) (0,1) is equal to 1008 \boxed{1008}

Hence the integral is nothing but,

1007 + 1008 = 2015 \boxed{1007 + 1008} = \boxed{2015}

The year we are in currently.

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