Question

If n=5q+4,then check weather n2-1 is divisible by 5, for some integer q

Answer 1

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Secondary School Math 5 points

If n= 5 q + 4 then check whether n×n -1 is divisible by 5 for some integer q.

Ask for details Follow Report by Joy109 08.04.2018

Answers

rpulenora0915 Virtuoso

N = 5q +4

n*n-1 = (5q +4) (5q +4) -1

= 25q^2 + 40q + 16 -1

= 25q^2 + 40q + 15

by taking the common factor out,

5 (5q^2 + 8q +3)

So it's a multiple of 5.

therefore it is divisible by 5 for all integers q.

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