Let P(n):

For n =1 is true,

P(1):

=

Since, P(n) is true for n =1

Now, For n = k

P(k): - - - - (1)

We have to show that,

Now,

= using equation (1)

=

Therefore, P(n) is true for n = k + 1

Hence, P(n) is true for all n ϵ N by PMI