# Math Help - How to deal with the summation?

1. ## How to deal with the summation?

See Attachment. I do not know how to expand the equation stated in the attachment. The "!" is very confusing me. I tried to expand the equation on my own and input values into it, but I can't get the correct value so I guess that I may do something wrong.
Can someone help me to expand that equation for me once? Thank you.

2. $\displaystyle !$ is the factorial symbol. Basically, if $\displaystyle n$ is a positive integer, then $\displaystyle n! = n \cdot (n-1) \cdot (n-2) \dots 3 \cdot 2 \cdot 1$