A Game of Brackets!

Calculus Level 4

0 91 x 2 1 2 d x 0 20 x 2 1 2 d x \large \frac{\displaystyle \int_{0}^{91} \lfloor \lfloor x^{2} \rfloor^{\frac{1}{2}}\rfloor dx }{\displaystyle \int_{0}^{20} \lfloor \lfloor x^{2} \rfloor^{\frac{1}{2}}\rfloor dx }

Let this ratio be one that condenses to 9 2 α β \displaystyle \large \frac{9}{2} \frac{\alpha}{\beta} where α \large \alpha and β \large \beta are coprime positive integers. Find the product α β \alpha \beta .


The answer is 1729.

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2 solutions

Sumanth R Hegde
Dec 23, 2016

The function x 2 1 2 \lfloor \lfloor x^{2}\rfloor^{\frac{1}{2}} \rfloor is just x \lfloor x\rfloor for positive x. On integrating this , we get α = 91 β = 19 \color{#3D99F6}\boxed{\alpha = 91} \ \color{#D61F06}\boxed {\beta = 19 } . Thus α β = 1729 \color{#20A900}\boxed{ \alpha\beta = 1729}

nice approach! and very colourful as usual!:P

Rohith M.Athreya - 4 years, 5 months ago

How do you do the colour?

Anirudh Chandramouli - 4 years, 5 months ago

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https://en.m.wikibooks.org/wiki/LaTeX/Mathematics . All details are here

Sumanth R Hegde - 4 years, 5 months ago

Perfect answer Rohith

Yeah! I knew u would be one of the first few to get it right :)

Rohith M.Athreya - 4 years, 5 months ago

Initially the limits were different(I think u intended it for x^2 ) and I got different answer. I kept wondering why I was wrong. Now I see it has been changed :P

Sumanth R Hegde - 4 years, 5 months ago

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yes, took me a few hours to figure out there was a small typo

Rohith M.Athreya - 4 years, 5 months ago

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:p. Just uploaded my solution.

Sumanth R Hegde - 4 years, 5 months ago

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I guess this would be level 3-4 then right?

Anirudh Chandramouli - 4 years, 5 months ago

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Yea I guess

Sumanth R Hegde - 4 years, 5 months ago

level 3-4-5 would be a wider estimate

Rohith M.Athreya - 4 years, 5 months ago

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