Lesson 5
1. Lesson 5
1.9. Explore 5
Module 1: Sequences and Series
Try This 5
In Try This 4 you most likely had to determine the number of terms in the series before using the geometric series formula you derived earlier in the lesson. Instead, you could have solved the problem by using a formula that doesn’t contain the variable n but will still find the sum of the series. You will create a formulato do this by combining two formulas in this Try This activity.
Using the formulas 
and tn = arn−1, try to construct a new formula that does not include the variable n. Need help? Take a hint.
Turn to pages 50 and 51 in the textbook to review an example of how the sum of a geometric series can be evaluated when you do not know how many terms are in the series. Two methods are presented. Which method do you prefer?
As you read, try to duplicate the results with your calculator. This will ensure you are entering the information into your calculator the right way.
Take a moment to add the alternate geometric series formula to your copy of Formula Sheet.
Self-Check 2
Complete Geometric Sum Formula Self-Check. Have some scrap paper handy to do rough work. You may wish to save your rough work in your course folder for future reference. If you make a mistake, don’t worry! You can reset each question, and then try again!