Solution:

Now putting n = 1, 2, 3, 4 we get,

a₁ = 6 – 1 = 5

a₂ = 6 – 2 = 4

a₃ = 6 – 3 = 3

a₄ = 6 – 4 = 2

∴ The sequence is 5, 4, 3, 2

We can see that,

a₂ – a₁ = 4 – (5) = -1

a₃ – a₂ = 3 – (4) = -1

a₄ – a₃ = 2 – (3) = -1

Since, the successive difference of list is same i.e -1

∴ The given sequence is in A.P