Question

Use sigma notation to represent the sum of the first seven terms of the following sequence: 4, 10, 16, … the summation from n equals 1 to 7 of negative 4 plus 6 times n the summation from n equals 1 to 7 of 4 plus 6 times n the summation from n equals 1 to 7 of 2 plus 6 times n the summation from n equals 1 to 7 of negative 2 plus 6 times n

Answer 1

$\bf 4~~,~~\stackrel{4+6}{10}~~,~~\stackrel{10+6}{16}~~,~~...~\hspace{10em}\stackrel{\textit{common difference}}{d = 6} \\\\[-0.35em] ~\dotfill\\\\ n^{th}\textit{ term of an arithmetic sequence} \\\\ a_n=a_1+(n-1)d\qquad \begin{cases} a_n=n^{th}\ term\\ n=\textit{term position}\\ a_1=\textit{first term}\\ d=\textit{common difference}\\[-0.5em] \hrulefill\\ a_1=4\\ d = 6 \end{cases} \implies a_n=4+(n-1)6 \\\\\\ a_n=4-6+6n\implies a_n=6n-2~\hfill \displaystyle\boxed{\sum\limits_{n = 1}^{7}~6n-2}$