Inverses

Basant is on the ground floor of Bela's Building of Fun. He is in a great hurry and by mistake presses +3. What can he do to cancel it and stay on the ground floor? He presses -3. Up three and down three cancel out: (+3) + (-3) = 0.

We call -3 the inverse of +3. (Its full name, which you will meet later, is the additive inverse.) In the same way, the inverse of -3 is +3. A number and its inverse always add up to zero. If Basant presses +4 and then -4, he ends up back on the ground floor, because (+4) + (-4) = 0.

Another way to see it: if you are on Floor +4 and press its inverse, -4, you are back at zero, the ground floor. If you are on Floor -2 and press its inverse, +2, then (-2) + (+2) = 0, the ground floor again.

So the inverse of +4 is -4, the inverse of -4 is +4, the inverse of +2 is -2 and the inverse of -1 is +1. What about 0? Pressing nothing needs nothing to cancel it: 0 + 0 = 0, so the inverse of 0 is 0 itself.