Question

Find the 7th term of the geometric sequence a3 =128,r=-1/4

Answer 1

Answer:

Step-by-step explanation:

The general formula for this sequence is a(n) = a(1)*(-1/4)^(n - 1).  We don't yet know a(1).

If a(3) = 128, then 128 = a(1)*(-1/4)^(3 - 1), or

128 = a(1)*(1/16)

and so a(1) = 128/16

resulting in the specific formua a(n) = 8(-1/4)^(n - 1)

Now let's find a(7):

a(7) = 8(-1/4)^1 * (-1/4)^(6)

or

a(7) = 8(-1/4)^7