What is the remainder when ( 2 2 0 1 4 + 7 × 5 4 0 2 0 ) is divided by 23?
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@Anik Mandal , next time, for ( m o d a ) notation, use the L A T E X code, you may want to see it, i've edited that in your solution.
By Fermat's little theorem , as 23 is a prime,
2 2 2 ≡ 1 ( m o d 2 3 ) ∴ 2 2 2 × 9 1 = 2 2 0 0 2 ≡ 1 ( m o d 2 3 ) ∴ 2 2 0 1 4 ≡ 2 1 2 ( m o d 2 3 )
Similarly doing for the second term, we have
5 4 0 0 4 ≡ 1 ( m o d 2 3 ) ∴ 5 4 0 2 0 ≡ 5 1 6 ( m o d 2 3 )
Moreover, we have
5 2 ≡ 2 5 ≡ 2 ( m o d 2 3 ) ⟹ 5 1 6 ≡ 2 8 ( m o d 2 3 )
So asked thing is reduced to finding 2 1 2 + 7 × 2 8 ( m o d 2 3 )
This is simple by following way, 2 1 2 + 7 × 2 8 ≡ 2 8 ( 2 4 + 7 ) ≡ 2 8 ( 2 3 ) ≡ 0 ( m o d 2 3 )
Great use of FLT!
I too did the same way ! !
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5 2 ≡ 2 ( m o d 2 3 )
5 4 0 2 0 ≡ 2 2 0 1 0 ( m o d 2 3 )
Hence 5 4 0 2 0 and 2 2 0 1 0 both leave the same reminder when divided by 2 3 .
So asked thing is reduced to finding 2 2 0 1 4 + 7 ⋅ 2 2 0 1 0 ( m o d 2 3 )
2 2 0 1 4 + 7 . 2 2 0 1 0
= 2 2 0 1 0 ( 2 4 + 7 )
= 2 2 0 1 0 . 2 3
Hence.the expression is divisible by 2 3 and leaves a remainder of 0 when divided by 2 3 .