Arnold Williams (notebuyer) wrote,
Arnold Williams
notebuyer

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Current Reading:

John Derbyshire's latest math book, Unknown Quantity, which discusses the history of algebra.

I know that for most people the word immediately brings a sense of panic, from your high school classroom, the teacher having asked you to solve something. It was just like fractions in grammar school, only worse. But this book, taken a little at a time (I don't have time for more than a few pages before my daughter requires my attention for something), can be quite fun.

Today's pearl: to show off to junior high students who already believe they know more math than you ever will (and they may be right).

How to multiply two numbers, a and b.

Add them together, and square the result. Call it the first result.

Subtract the smaller from the larger, and square the result. Call it the second result.

Subtract the second result from the first result, and divide by 4. The number you have is the product of multiplying a and b.

You have multiplied two different numbers using squaring, subtraction, and division. Not too shabby.

I know, the long way around -- why not just use a calculator? The proces was invented in Babylon, where not only were there no calculators, but there were no numbers that were useful for multiplication (their base was 60, not 10 -- if you thought our "times tables" were hard, imagine what they faced: then smile and realize that this is why they invented this in the first place. You can put pebbles on the floor and make squares, add pebbles, take away pebbles, and dividing the resulting pebbles into a square and quartering it is pretty easy. Arithmetic for those who like messy solutions.
Tags: math
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