Write the sum
using summation notation.
The nth term is
We want to start at n = 0, and keep going forever and ever...and ever. Instead, we write
Use summation notation to write the series
5(0.3)5 + 5(0.3)6 + 5(0.3)7 + ....
We could say the series starts at n = 5, since that's the exponent of the first term:
Then we would write the series as
Alternatively, we could decide we wanted to write the series starting at n = 0. In this case we'd think of the general term as
Make it rain.