Question

A binary operation x defined on the set of integers is such that m x n =m+n+mn for all the integers m and n. Find the inverse of -5 under the operation, if the Identity element is o?

Answer 1

we want n = m^-1, so that means -5 x n = 0
-5 x n = -5 + n - 5n = -5 - 4n
n = -5/4
am I missing something? n should be an integer
maybe the set of integers is not closed under "x"

Answer 2

Wow. Very correct