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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!