The explicit formula for a geometric sequence is a_n = a_1 * r^(n-1). The variable a_n is equal to the value of the nth term in the given geometric sequence, while a_1 is the value of the first term in the sequence.
In the explicit formula for a geometric sequence, the variable r represents the common ratio for the sequence. For example, in the sequence 2/1, 4/2, 6/3, the common ration is 2. The variable n indicates the number term in the sequence that the equation is evaluating. In the above sequence, n = 3 when evaluating 6/3, the third term in the series.