I have a set of questions like the following:

For the function , find the term containing and hence express the expansion in sigma notation.

The answer for this particular problem is given at the back of the book as

I get that there is some manipulation of the binomial coefficient, but I am wondering if there is a standard approach to these types of problems, and it confuses me that r still goes to 9 when there should now be 11 terms it seems.

Thoughts appreciated.

Andrew