Put n = 1

A₁= 5(1) – 7

= -2

Put n = 2

A₂= 5(2) – 7

= 10 – 7 = 3

Put n = 3

A₃= 5(3) – 7

= 15 – 7 = 8

Common difference, d₁= a₂ – a₁= 3 – (-2) = 5

Common difference, d₂= a₃ – a₂= 8 – 3 = 5

Since, d₁ = d₂ and Common difference = 5

Therefore, it’s an A.P.