## Algebra 1: Common Core (15th Edition)

a) $2,4,8,16,...$ The starting value is 2. The common ratio r is $\frac{4}{2}=2$ The recursive formula is $a_1=2; a_n=a_{n-1}.2$ The explicit formula is $a_n=2.2^{n-1}$ a) $40,20,10,5,...$ The starting value is 40. The common ratio r is $\frac{20}{40}=\frac{1}{2}$ The recursive formula is $a_1=40; a_n=a_{n-1}.\frac{1}{2}$ The explicit formula is $a_n=40.\frac{1}{2}^{n-1}$