In the given question we need to find the sum of the series.
For that, first, we need to find the nth term of the series so that we can use summation of the series with standard identities and get the required sum.
The series given is 3, 15, 35, 63 … to n terms.
Now, we need to find the sum of this series, Sn.
Note:
So, for the given series, we need to find,