Let P(n):

For n= 1 is true,

P(1):

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

Let P(n) is true for n = k, so

- - - - (1)

We have to show that,

Now,

=

=

=

=

=

=

=

=

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

Hence, P(n) is true for all n∈N