Date: 10/07/2002 at 21:12:13 From: Amy W. Subject: Multiplication signs Why are there four different ways to indicate the operation of multiplying? x, parenthesis, dot, and numbers beside each other? I think x can't always be used because sometimes it's a variable in an equation. I don't know why all these ways mean multiplication.
Date: 10/07/2002 at 23:18:51 From: Doctor Peterson Subject: Re: Multiplication signs Hi, Amy. The different symbols arose through history, and although each new symbol filled a need, the old symbols still had advantages in some circumstances, so they have been retained. It does get confusing though, doesn't it? This page tells some of the history of these symbols: Earliest uses of mathematical symbols http://jeff560.tripod.com/operation.html You will find here that the cross was the first multiplication symbol. It is retained now primarily for elementary students, since it is more distinctive than the other symbols. The dot was introduced because the cross was too similar to an x, so once we get into algebra we tend to drop the cross - until we get into vector algebra. Then both "dot product" and "cross product" are defined. It was lucky there were two symbols available when vectors were invented. "Juxtaposition," or putting two variables, or a number and a variable, next to each other, actually preceded any of the symbols. It essentially arises from natural language, where we say "two x's," leading us to write "2x." That can't be used when we multiply two numbers, unless we put at least one of them in parentheses, so we can't easily drop symbols entirely. But using this symbolism whenever possible saves a lot of ink. I would not call parentheses a way to show multiplication, but just a way to either hold an expression together so the whole thing is multiplied, or to separate two numbers that are being multiplied by juxtaposition. - Doctor Peterson, The Math Forum http://mathforum.org/dr.math/
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