## Ask Professor Puzzler

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Shawna from Michigan asks, "The upper case sigma symbol is used for summation, but I've also seen the upper case pi symbol used in a similar way. What does that mean?"

Hi Shawna. The answer is pretty short and straight-forward. The pi symbol, when used that way, means multiplying a set of numbers (instead of adding them).

If you're wondering why pi is used, the reason is simple; it's the same reason we use sigma for sums. S for sigma, S for sum. P for Pi, P for product.

Here's an example; take a look at this expression:

This means that we multiply together all the numbers we get by plugging in x = 3, x = 4, x = 5, and x = 6.

The numbers are:

3 - 2 = 1

4 - 2 = 2

5 - 2 = 3

6 - 2 = 4

So the product is 1 x 2 x 3 x 4 = 24

Of course, that was a fairly simple problem, and they can get a lot more complicated (interesting) than that. But that will be sufficient to answer your question, I think!

Professor Puzzler