Disprove with the counter example: If a^2 = b^2 (mod n) then a=b (mod n)..

where "=" means the equivalence.

I think...since, n\a^2 - b^2...proceeds to n\(a-b)(a+b)...shows that n also divides (a-b)...so can't we directly say that a=b (mod n)..??

how do I do this one?

Thanks for any help!