In order to write a series in sigma notation you must:
Identify the index of summation and first value. In the equation, the index of summation would be i and the first value is assumed to be 1 due to the pattern that can be traced back.
Identify the last value of n, which would be 7 in the series. This value is placed as a superscript next to or above the capital Greek letter ∑.
Identify the formula for the terms. In thes case, the formula for the terms is (7+8i) because there are seven terms in the sequence that are increasing by 8. The variable i comes after because that is the letter used in the index of summation.
