Question

The sum of n terms of an AP is 3n2 + 5n, which term of AP is 164. (a) 25 (b) 27 (c) 29 (d) 31

Answer 1

Sn=3n2 +5n

S1=a1=3(1)2+5(1)=8

S2=3(2)2+5(2)=22

S2=22=a1+a2

a2=22-8=14

d=a2-a1=14-8=6

nth term=a+(n-1)d

164=8+(n-1)6

164-8 / 6=n-1

156/6=n-1

26+1=n

n=27

So 27th term is 164.