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

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

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

Answer: (A)

In sigma notation, you sum over an index that runs through consecutive integers. The number below the sigma is the starting value of that index—the lower limit. The sum continues up to the value above the sigma, which is the upper limit. For example, sum with a lower limit 3 and an upper limit 7 means you add the terms for the index values 3, 4, 5, 6, and 7. So you’re starting at 3 and ending at 7, and the number of terms is 7 − 3 + 1 = 5. If the upper bound is infinity, the sum goes on indefinitely. This is why the number below the sigma indicates the starting point of the summation.

In sigma notation, you sum over an index that runs through consecutive integers. The number below the sigma is the starting value of that index—the lower limit. The sum continues up to the value above the sigma, which is the upper limit. For example, sum with a lower limit 3 and an upper limit 7 means you add the terms for the index values 3, 4, 5, 6, and 7. So you’re starting at 3 and ending at 7, and the number of terms is 7 − 3 + 1 = 5. If the upper bound is infinity, the sum goes on indefinitely. This is why the number below the sigma indicates the starting point of the summation.