Given: α,β are roots of x2−x−1=0.
⇒α2−α−1=0
⇒α2=α+1...(i)
Also, Sn=2023αn+2024βn
⇒Sn−1+Sn−2=2023αn−1+2024βn−1+2023αn−2+2024βn−2
⇒Sn−1+Sn−2=2023αn−2(1+α)+2024βn−2(1+β)
Using equation (i),
⇒Sn−1+Sn−2=2023αn−2(α2)+2024βn−2(β2)
⇒Sn−1+Sn−2=2023αn+2024βn
⇒Sn−1+Sn−2=Sn
Putting, n=12
⇒S12=S11+S10