Here is the graph of an exponential function corresponding to a geometric sequence. which of the following is the explicit formula for the geometric sequence .

Based on the graph, it can be said that the initial value of the sequence falls on number 8 until it reaches down asymptotic to the x-axis to value corresponding to n. In a geometric sequence, the value of nth term, denoted by an is equal to the product of the first element of the sequence and the common ratio raised to n-1. Therefore, the explicit formula for the geometric sequence above is,
an = 8(1/2)^n-1 (option a)