**I've been working through this binomial question in my notes and there is one step I'm not entirely sure about. When it comes to the point of combining the two series into one I'm fairly certain what's in my notes is incorrect so I'd like to fix it.** **It's safe to assume that all the work up to this point is correct. (See figure)**
How do I combine these two series into 1?

I think my professor tried to do something like a common denominator but I can't follow his work.

Someone care to show me (In slow steps

) how I can combine the two and simplify?

Thanks again!