Find the sum of the first 8 terms of the sequence. 1, -3, -7, -11, ...

Answer 1

The sequence is 1,-3,-7,-11,...............

The sequence is arithmetic sequence.

Calculate the common difference,

d = second term - first term

   =-3-1 = -4

First term a =1

Number of terms n = 8

Calculate the sum of the sequence by using the formula.

Sn =n/2(2a+(n-1)d)

     =8/2(2(1)+(8-1)(-4))

     = 4 (2+(7)(-4))

      = 4 (2+(-28))

     = 4 (-26)

     = - 104

Therefore, the sum of the 8 terms is -104