Question

Write an explicit formula for the sequence . Use this to find the 80th term of the sequence that begins -3 , 1 , 5 , 9

Answer 1

A n = 4n - 7

Explanation:

Answer 2

`\bf -3~~,~~\stackrel{-3+4}{1}~~,~~\stackrel{1+4}{5}~~,~~\stackrel{5+4}{9}...\qquad \stackrel{\textit{common difference}}{d=4} \\\\\\ n^(th)\textit{ term of an arithmetic sequence} \\\\ a_n=a_1+(n-1)d\qquad \begin{cases} a_n=n^(th)\ term\\ n=\textit{term position}\\ a_1=\textit{first term}\\ d=\textit{common}\\ \qquad \textit{difference}\\ \cline{1-1} d=4\\ a_1=-3 \end{cases}\implies a_n=-3+(n-1)4 \\\\\\ a_n=-3+4n-4\implies a_n=4n-7`