Essentially this is asking you to sum the first three values of the geometric series that starts with i being 1 and has the rule of ().
Since we must sum the first <em>three </em>geometric values we need to see what the value of i will be for the first three. The sigma notation shows us that the first i will be equal to 1. This means the second i is 2 and the third i is 3.
Knowing this you can plug in the corresponding i values into () and sum it all together
() + (
) + (
)
() + (
) + (
)
() + (
) + (
)
(8) + (2) + ()
10 +
10.5
Hope this helped!
~Just a girl in love with Shawn Mendes