Question

3. Find the sum of each arithmetic series
(i) 38 + 35 + 32 +........+2

Answer 1

First we have to know that how many terms are there in the above series.

   a = 38    d = t₂ - t₁          L = 2

                d = 35-38

                   = -3

     n = [(L-a)/d] + 1

       = [(2-38)/(-3)] + 1

       = [(-36)/(-3)] + 1

       = 12 + 1

    n = 13

   S n = (n/2) (a+L)

        = (13/2) (38 + 2)

        = (13/2) (40)

        = (13) (20)

        = 260

Answer 2

Hope it is helpful ✌