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Multiplication sign
The multiplication sign (×) is very old. It comes from India, where it was created after the frequent use of cross-multiplication, as in
where you start to calculate from top left to bottom right and then from bottom left to top right
. This results in a movement that looks like a cross
.
Explanation
Everybody knows the multiplication tables, and so you know immediately the outcome of
Often you don't even have to write a multiplication sign, because everything is clear enough, as with
and you must therefore describe it as: x times x plus 4. Also the simple notation
is a multiplication, because it means: 3 times x. Rather tricky is
because here you multiply 156 with √6 and with x. But after some time you won't notice this anylonger and even a difficult term poses no problems, just look at
Other notations
Mathematicians prefer to write the multiplication sign as a point, to avoid confusion with the letter x, so
x · x instead of x × x
Sometimes you must use an asterisk (∗) because a point has the meaning of 'decimal point', and then you get
On calculators, smartphones and tablets you will normally see a × key, sometimes also a ∗ key.