[tex]\bf 7~~,~~\stackrel{7-4}{3}~~,~~\stackrel{3-4}{-1}~~,~~\stackrel{-1-4}{-5}~~,~~\stackrel{-5-4}{-9}~~,~~...[/tex]
so namely, the "common difference" d = -4, and the first term a₁ = 7.
[tex]\bf n^{th}\textit{ term of an arithmetic sequence}
\\\\
a_n=a_1+(n-1)d\qquad
\begin{cases}
n=n^{th}\ term\\
a_1=\textit{first term's value}\\
d=\textit{common difference}\\
----------\\
d=-4\\
a_1=7
\end{cases}
\\\\\\
a_n=7+(n-1)(-4)\implies a_n=7+(4-4n)
\\\\\\
a_n=11-4n\implies a_n=-4n+11[/tex]
