Question

sn=8n-2 then find the a4 . it is in Ap.


is the answer is 22. is this correct or not ​

Answer 1

GIVEN that

Sₙ = 8 n -2

so,

sum of first term will give us first term

i.e,

a₁=S₁

a₁ = 8 (1) -2

a₁=8-2

a₁=6 (= a,first term)

NOW ,

S₂ = a₁ + a₂

8 (2) - 2 = 6 + a₂

14 = 6 + a₂

a₂ = 14-6

a₂ = 8

NOW,

S₃= a₁ + a₂ + a₃

8 ( 3) -2 = 6 + 8 + a₃

a₃ = 22 - 14

a₃ = 8

now we can easily see in a₁ , a₂ , a₃ that the common difference is not same hence,eqn that Sₙ = 8 n -1 is not correct to find the sum of n terms of AP and a₁ , a₂ , a₃ does not form an AP.