LET’S TRY ONE
Find the sum of the first 5 terms of an arithmetic sequence whose first term is 2 and common difference is 3.
40
The last term is 14. Sum = 5(2+14)/2 = 40.
Learning steps & teaching tips
Use equal-sum pairs to find a finite arithmetic series.
- Find the last term, average the first and last, then multiply by the number of terms.
- Work through the example and explain why each operation is used.
- Estimate or use another method to check the result before choosing.
Try it together
Work with a partner: solve one example, explain the method, then change one number and predict what changes.
Find the last term, average the first and last, then multiply by the number of terms.