What is the opposite of one-half?

Answer 1

That depends what you mean with "opposite". Two important math concepts are:

a) The additive inverse. That's the same number, with a minus in front of it (a number plus its additive inverse = 0).

b) The multiplicative inverse, also called the reciprocal. One divide by the number. For a fraction, you can simply exchange numerator and denominator to get the reciprocal. (A number times its reciprocal = 1.)