Possibility of inductive proof on leading term?

I actually have two questions on the following problem:

It is known that the leading term of the sum is , and for the the leading term is . Can you make a guess what's the leading term in ? in ? Can you prove something inductively for this?

Clearly the guess is the leading term would be:

However, I have two questions here.

1) I don't really understand what this problem means by "leading term". If there are no variables in the sum, how can there be terms?

2) I couldn't find anywhere in my text if an inductive proof applies for just proving a leading term. Does it?

Thank you in advance for your help.