In sigma notation, what does the number above the sigma represent?

In sigma notation, what does the number above the sigma represent?

• A. The upper limit of summation
• B. The lower limit of summation
• C. The number of terms
• D. The starting term index

Answer: (A)

Sigma notation sums a sequence by letting an index run from a starting value up to an ending value. The number written above the sigma is the ending value, the upper limit, which sets the largest index included in the sum. The number below is the starting value, the lower limit, which sets the smallest index included. If the step between terms is 1, the total number of terms is the upper limit minus the lower limit plus one. So the top number is about where the index stops, not about how many terms there are or the starting index. For example, summing i from 2 to 5 includes i = 2, 3, 4, 5, giving four terms.

Sigma notation sums a sequence by letting an index run from a starting value up to an ending value. The number written above the sigma is the ending value, the upper limit, which sets the largest index included in the sum. The number below is the starting value, the lower limit, which sets the smallest index included. If the step between terms is 1, the total number of terms is the upper limit minus the lower limit plus one. So the top number is about where the index stops, not about how many terms there are or the starting index. For example, summing i from 2 to 5 includes i = 2, 3, 4, 5, giving four terms.