Find [tex] a_{1} [/tex] by plugging in 1 into n:
[tex] a_{1} = 98-2(1)=96[/tex]
Find [tex] a_{11 [/tex] by plugging in 11 into n:
[tex] a_{11} = 98-2(11)[/tex]
[tex] a_{1} =98-22=76[/tex]
Now to find the sum your formula is:
[tex] S_{n} = \frac{n}{2} ( a_{1} + a_{n}) [/tex]
[tex] n = 11, a_{1} = 96 , a_{11} =76[/tex]
Now plug that into the formula
[tex] S_{11} = \frac{11}{2} (96+76)[/tex]
[tex] S_{11} = 5.5(172)=946[/tex]
Hope that helps
