Find the sum of the following arithmetic progressions:

… upto 11 terms.

The arithmetic progression …. is given.
Here first term is and common difference is .
Since the sum of n terms is
S_{n =}

Where,

a = First term of AP
d = Common difference of AP
and no of terms is ‘n’

So sum of first 11 terms S₁₁

Hence, Sum of first 11 terms is .