Exercise 26 Page 319

The explicit formula of a geometric sequence combines the information provided by the two equations of the recursive form into a single equation. Recursive: a_1&= a_1; a_n= r* a_(n-1) Explicit: a_n&= a_1 * r^(n-1) In these formulas, r is the common ratio and a_1 is the first term. Looking at the given recursive formula, we can identify the common ratio r and the value of the first term a_1. a_1= -2; a_n= 9a_(n-1) We can see that 9 is a common ratio and -2 is the first term. Now we have enough information to form an explicit formula for this sequence.