Question

algebraic expression sn = 3n2+ 2n​

Answer 1

Answer:

an = Sn − Sn-1

Given,

Sn = 3n2 + 2n

∴ Sn-1 = 3(n − 1)2 + 2(n − 1)

(∴ an = Sn − Sn-1)

∴ an = 3n2 + 2n − {3(n − 1)2 + 2(n − 1)}

= 3n2 + 2n − {3(n2 − 2n + 1) + 2n − 2} =

3n2 + 2n − {3(n2 − 6n + 3 + 2n − 2} =

3n2 + 2n − {3(n2 − 4n + 1} =

6n − 1

Hence,

a2 = 6(2) − 1 = 11