I'm going through Knapp's book on elliptic curves and I got stuck in a minor detail.
This is a part of the proof of Proposition 2.12:
I could understand everything except for this little detail: Where are we making use of the assumption $d>2$?
I will post some pictures about the references that the proof makes use of, in order for you to understand the whole argument.
Proposition 2.7 and identity (2.12):