δ = Z + L
where Z = (±)N/S(90°-AN/S) with upper/lower case
for altitude AN/S measured positive from due north/south.
So
δ = (±)N/S(90°-AN/S) + L and AN/S = 90°+(±)N/S(L-δ) and L = δ + (±)N/S(AN/S-90°)
The formula for the altitude of the NCP/SCP is
AN/S = 90°+(±)N/S(L-(±)NCP/SCP90°)
To be explicit:
AN(NCP)=L AS(NCP)=180°-L
AS(SCP)=180°+L AS(SCP)=-L