Answer:
a[n] = 2^(4-n)
Step-by-step explanation:
There are many ways the formula for the given sequence can be written. The first term (a[1]) is 8 and the common ratio (r) is 1/2, so the generic form is ...
a[n] = a[1]·r^(n-1)
a[n] = 8·(1/2)^(n-1)
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If we recognize that 8 = 2^3 and 1/2 = 2^-1, then we can write this as ...
a[n] = 2^3·(2^-1)^(n-1) = 2^(3 -n +1)
a[n] = 2^(4 -n)
