Celinee West - Flywheelsites News
= 1 from first principles why does 0! All i know of factorial is that x! Is equal to the product of all the numbers that come before it.
Is there a formal proof for $(-1) \\times (-1) = 1$? It's a fundamental formula not only in arithmetic but also in the whole of math. Is there a proof for it or is it just assumed?
