What number is equal to it opposit?

Answer 1

The number that is its own "additive inverse" is zero. (x + 0 = x - 0)

For the multiplicative inverse (1/x), the number 1 is its own inverse (also -1). (x times 1 = x/1)

x = 1/x is only true where x = 1 or x = (-1)

Answer 2

0 is the same as its additive inverse.

+1 and -1 are the same as their multiplicative inverses (respectively).