P.S.

A couple of thoughts occurred to me after I sent a message.

The first one has nothing to do with Mathematics. Just consider the following sentence:

Can you figure out its meaning?

The second is a variation on the theme from the previous message. Let your daughter stand facing a wall. Then ask her to turn left through 180^o. Now her back will be to the wall. If she makes exactly same movement twice she'll face the wall again. In other words, she'll be in the same position as before turning twice.

I must remark that calling -a "negative a" is an unfortunate misuse of notations which is widely spread through the whole education establishment. I prefer "minus a" instead. The reason is two-fold.

1. For one, a could be negative to start with. Then -a is a positive number. So that calling it negative a which has a connotation of being negative, is often misleading.
2. Secondly, being negative indicates a state of a quantity, and thus is static. Minus a connotes a modification of a given number a with the possibility that the result might as well be positive. A double modification (like going back and force) may change nothing.

Copyright © 1996-2010 Alexander Bogomolny

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