Answer :

SOLUTION

Series given:

[tex]9+12+15+18+21+24[/tex]

First, find an nth expression for this series

[tex]\begin{gathered} T_n=a+(n-1)d \\ a=9 \\ d=12-9=3 \\ d=3 \\ \text{Therefore, the nth term will be:} \\ 9+(n-1)3 \\ 9+3n-3 \\ 6+3n \end{gathered}[/tex]

To write the sigma notation:

1. We need to know the nth term expression as we have solved above

2. We need to know the number of terms in the series = 6

The sigma notation therefore is:

[tex]\sum ^6_{n\mathop=1}(6+3n)[/tex]

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