To prove - congruence of numbers is an equivalence relation
Let us take a line segment AB of length n and a scale of 3 m to measure it
In this way we can easily prove it when it is reflexive,symmetric and transitive.
i) It is reflexive if we take the point A itself,it measures 0 m and 0 is multiple of every number
ii) It is symmetric because if we take the length between point A and B and if it is divisible by 3, then it is obviously true that the length between point B and A is also divisible by 3
iii) It is also transitive because if we make an extra point C outside AB and the length AB is divisible by 3 and the length BC is divisible by 3 then it is also true that AC is divisible by 3
Thus it proves that congruency of numbers is an equivalence relation