Question

The sum of n terms of an ap is 3n square +2n.Find the series and the 10th term

Answer 1

Sn = 3n²+2n

Let n be 1

S1 = 3(1²)+2(1) = 3+2 = 5

a1 = 5

Let n be 2

S2 = 3(2²)+2(2) = 12+4 =16

S2 = a1+a2 = 16

5+a2 = 16

a2 = 11

d = a2-a1 = 11-5 = 6

d = 6

AP:5,11,...

a10 = a +9d = 5+54 = 59

a10 = 59