Put n = 1

A₁= 3(1)² – 5 = 3 – 5 = -2

Put n = 2

A₂= 3(2)² – 5 = 12- 5 = 7

Put n = 3

A₃= 3(3)² – 5 = 27 – 5 = 22

Common difference, d₁= a₂ – a₁ =7 – (-2) = 9

Common difference, d_{2 =} a₃ – a₂ = 22 – 9 = 13

Since, d₁ ≠ d₂

Therefore, it’s not an A.P.