Chapter 12 Sequences and Series - 12.5 Use Recursive Rules with Sequences and Functions - 12.5 Exercises - Problem Solving - Page 832: 47b

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$$a_n+d=0.7a_{n-1}+20+d\\a_n+d=0.7(a_{n-1}+\frac{20+d}{0.7})\\\rightarrow d=\frac{20+d}{0.7}=\frac{200}{3}$$ The maintenance level of this drug is $a_n-\frac{200}{3}=0.7(a_{n-1}-\frac{200}{3})\\a_n \rightarrow \frac{200}{3}$