Yet Another Remainder Problem!

201 4 2014 201 5 2015 201 6 2016 201 7 2017 201 8 2018 201 9 2019 202 0 2020 202 1 2021 202 2 2022 \begin{vmatrix} 2014^{2014} & 2015^{2015} & 2016^{2016} \\ 2017^{2017} & 2018^{2018} & 2019^{2019} \\ 2020^{2020} & 2021^{2021} & 2022^{2022} \end{vmatrix} Find the remainder when the determinant above is divided by 5.


The answer is 4.

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1 solution

Chew-Seong Cheong
Feb 21, 2017

201 4 2014 201 5 2015 201 6 2016 201 7 2017 201 8 2018 201 9 2019 202 0 2020 202 1 2021 202 2 2022 ( 2015 1 ) 2014 201 5 2015 ( 2015 + 1 ) 2016 ( 2015 + 2 ) 2017 ( 2020 2 ) 2018 ( 2020 1 ) 2019 202 0 2020 ( 2020 + 1 ) 2021 ( 2020 + 2 ) 2022 (mod 5) ( 1 ) 2014 0 1 2016 2 2017 ( 2 ) 2018 ( 1 ) 2019 0 1 2021 2 2022 (mod 5) 1 0 1 2 2017 2 2018 1 0 1 2 2022 (mod 5) 2 2040 + 2 2017 + 1 (mod 5) Since gcd ( 2 , 5 ) = 1 , Euler’s theorem applies. 2 2040 mod ϕ ( 5 ) + 2 2017 mod ϕ ( 5 ) + 1 (mod 5) Euler’s totient function ϕ ( 5 ) = 4 2 2040 mod 4 + 2 2017 mod 4 + 1 (mod 5) 2 0 + 2 1 + 1 (mod 5) 1 + 2 + 1 (mod 5) 4 (mod 5) \begin{aligned} \begin{vmatrix} 2014^{2014} & 2015^{2015} & 2016^{2016} \\ 2017^{2017} & 2018^{2018} & 2019^{2019} \\ 2020^{2020} & 2021^{2021} & 2022^{2022} \end{vmatrix} & \equiv \begin{vmatrix} (2015-1)^{2014} & 2015^{2015} & (2015+1)^{2016} \\ (2015+2)^{2017} & (2020-2)^{2018} & (2020-1)^{2019} \\ 2020^{2020} & (2020+1)^{2021} & (2020+2)^{2022} \end{vmatrix} \text{ (mod 5)} \\ & \equiv \begin{vmatrix} (-1)^{2014} & 0 & 1^{2016} \\ 2^{2017} & (-2)^{2018} & (-1)^{2019} \\ 0 & 1^{2021} & 2^{2022} \end{vmatrix} \text{ (mod 5)} \\ & \equiv \begin{vmatrix} 1 & 0 & 1 \\ 2^{2017} & 2^{2018} & -1 \\ 0 & 1 & 2^{2022} \end{vmatrix} \text{ (mod 5)} \\ & \equiv 2^{2040} + 2^{2017} + 1 \text{ (mod 5)} \quad \quad \small \color{#3D99F6} \text{Since }\gcd(2,5) = 1 \text{, Euler's theorem applies.} \\ & \equiv 2^{2040 \color{#3D99F6} \text{ mod }\phi(5)} + 2^{2017 \color{#3D99F6} \text{ mod }\phi(5)} + 1 \text{ (mod 5)} \quad \quad \small \color{#3D99F6} \text{Euler's totient function }\phi(5) = 4 \\ & \equiv 2^{2040 \color{#3D99F6} \text{ mod }4} + 2^{2017 \color{#3D99F6} \text{ mod }4} + 1 \text{ (mod 5)} \\ & \equiv 2^{\color{#3D99F6}0} + 2^{\color{#3D99F6}1} + 1 \text{ (mod 5)} \\ & \equiv 1 + 2 + 1 \text{ (mod 5)} \\ & \equiv \boxed{4} \text{ (mod 5)} \end{aligned}

Absolutely correct Approach

Md Zuhair - 4 years, 3 months ago

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You can use \ begin{vmatrix} \ end{vmatrix} for determinant.

Chew-Seong Cheong - 4 years, 3 months ago

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Thankyou sir. I will remember it.

Md Zuhair - 4 years, 3 months ago

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@Md Zuhair I learnt it from here

Select the symbols and the codes will be shown below.

Chew-Seong Cheong - 4 years, 3 months ago

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@Chew-Seong Cheong Yes, Sure.

Md Zuhair - 4 years, 3 months ago

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