Assumption $d>2$ on Proposition 2.12 from Knapp’s Elliptic Curves

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):

Lemma 2.11:

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