I will assume that the "-1" MountEvariste is concerned about is from another problem.
(That's one of the many reasons why it is much better to type a problem in rather than post a picture.)
Do you know about "getting a common denominator" in order to add fractions?
Do you know that $r^2- 2r= r(r- 2)$ and that $r^2- 4= (r- 2)(r+ 2)$?
So what is a common denominator for these fractions?