Too many ceilings

Algebra Level 4

( ( ( { x } + { x } + { x } ) + { x } ) ) ! \large \left (\lceil(\lceil(\{\lceil x \rceil\}+\lceil \{x\} \rceil +\{x\})\rceil + \{x\})\rceil \right)!

Find the value of the expression above, where x x is an irrational real number.

If you believe there are multiple values, submit your answer as 12345.

Notations :

  • \lceil \cdot \rceil denotes the ceiling function .

  • { } \{ \cdot \} denotes the fractional part function .

  • ! ! denotes the factorial notation. For example, 8 ! = 1 × 2 × 3 × × 8 8! = 1\times2\times3\times\cdots\times8 .


The answer is 6.

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3 solutions

Sabhrant Sachan
May 16, 2016

The best way to solve this problem is to break x x into its components .

Let x = I + f x=\color{#20A900}I+\color{#624F41}f where I \color{#20A900}I is the Integral part of x x and f \color{#624F41}f is the fractional part of x x such That 0 < f < 1 0<\color{#624F41}f<1 . Now ,

x = I + f = I + 1 { x } = { I + f } = f { x } = f = 1 { x } = { I + 1 } = 0 Putting the Values in the expression , we get ( ( ( 0 + 1 + f ) + f ) ) ! ( ( 1 + f + f ) ) ! ( ( 2 + f ) ) ! ( 3 ) ! = 6 \lceil x \rceil = \lceil \color{#20A900}I+\color{#624F41}f \rceil = \color{#20A900}I+1 \\ \{ x \} = \{ \color{#20A900}I+\color{#624F41}f \} = \color{#624F41}f \\ \lceil \{ x \} \rceil = \lceil \color{#624F41}f \rceil = 1 \\ \{ \lceil x \rceil \}= \{ \color{#20A900}I+1 \} = 0 \\ \text{Putting the Values in the expression , we get } \\ \implies ( \lceil ( \lceil(0+1+\color{#624F41}f) \rceil +\color{#624F41}f) \rceil)! \\ \\ \implies ( \lceil ( \lceil 1+\color{#624F41}f \rceil +\color{#624F41}f) \rceil)! \\ \implies ( \lceil (2 +\color{#624F41}f) \rceil)! \implies (3)! = \color{#3D99F6}{\boxed{6}}

Nice write up, Sambhrant!

Geoff Pilling - 5 years, 1 month ago

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Thank You Sir ! :D

Sabhrant Sachan - 5 years, 1 month ago

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Great explanation.

Ashish Menon - 5 years ago

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@Ashish Menon thanks Ashish

Sabhrant Sachan - 5 years ago

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@Sabhrant Sachan ¨ \Huge \ddot\smile

Ashish Menon - 5 years ago

Nice coloring :D

展豪 張 - 5 years, 1 month ago

This is the best way to do it, nice explanation!

tytan le nguyen - 5 years ago
Ashish Menon
May 17, 2016

x \left \lceil x \right \rceil is always an integer and fracrional function of any integer is always 0. So { x } \{ \left \lceil x \right \rceil \} = 0.
Now, { x } \{x\} always lies between 0 and 1. It can be 0 when it is an integer but x being irrational can never give its fractional function as 0. So for any values lying between 0 and 1, the floor function is always 1. So, { x } \left \lceil \{x\} \right \rceil = 1.

Now, { x } \{x\} is always less than 1 but greater than 0 for any irrational number as explained above. So, its value is 0.something.
So, evaluating the inner bracket, { x } + { x } + { x } \{ \left \lceil x \right \rceil \} + \left \lceil \{x\} \right \rceil + \{x\} = 1.something. Now, the floor of this value is 2. So, ( { x } + { x } + { x } ) = 2 \left \lceil \left( \{ \left \lceil x \right \rceil \} + \left \lceil \{x\} \right \rceil + \{x\} \right) \right \rceil = 2 .

Again, { x } \{x\} is always less than 1 but greater than 0 for any irrational number as explained above. So, its value is 0.something.
So, ( { x } + { x } + { x } ) + { x } \left \lceil \left( \{ \left \lceil x \right \rceil \} + \left \lceil \{x\} \right \rceil + \{x\} \right) \right \rceil + \{x\} = 2.something.

So, ( ( { x } + { x } + { x } ) + { x } ) = 3 \left \lceil \left( \left \lceil \left( \{ \left \lceil x \right \rceil \} + \left \lceil \{x\} \right \rceil + \{x\} \right) \right \rceil + \{x\} \right) \right \rceil = 3 .

So, the answer which we want is the factorial of the above expression which is 3! = 6 \boxed{6} .

Goh Choon Aik
May 18, 2016

What I did was plug in pi and derive the answer from there. But there are fancy explanations that tells you why it works above and/or below me!

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