Prove that a congruent b(modn) if and only if a^2 + b^2 congruent 2ab(mod n^2)
Help please
let's take first
we have want the right side
this mean and this mean there exist an integer x such that
so
simplify the left side
now we have
so there exist an integer y such that
note that y is square can you prove it ??
so we can write y=c^2
by taking square root
proof ends