Question

The sum of n terms of an A.P. is 2n+3n^2. Which term is of this A.P is equal is equal to 299

Answer 1

Answer:

Given that

Sum of n terms = Sn = 2n + 3n²

S1 = 2(1) + 3(1)² = 5

Sum of 1st term is same as first term so a1 = a = 5

S2 = 2(2) + 3(2)² = 4 + 12 = 16

S2 = a1 + a2

16 = 5 + a2

⇒ a2 = 11

Common difference d = a2 - a1 = 11 - 5 = 6

A.P is 5 , 11 , 17 , 23 , 29 .......

rth term ar = ( 5 + ( r-1)6)

⇒ 5 + 6r - 6

⇒ 6r - 1 is rth term of A.P