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
