what is the multiplicitive inverse

In simple terms, it's the reciprocal of a number such that, when we multiply the number by that reciprocal, we get 1.

For instance, the multiplicative inverse of 3 is 1/3 because  3 * (1/3)  = 1.

And the multiplicative inverse for a fraction a/b is b/a because (a/b)*(b/a) = 1

So, in general, the multiplicative inverse of a number, n, is just 1/n .

Note that 0 doesn't have a multiplicative inverse because 1/0 isn't defined.