Which Term?
Part of the Exponentials, Logs & Sequences section of Coddy's Algebra 2 journey. Lesson 37 of 49.
The rule turns a position into a term. Sometimes you know the term and want the position. In 4, 9, 14, ..., the rule is a(n) = 4 + (n - 1) × 5. Which term is 79?
Set the rule equal to 79 and solve for n: 4 + (n - 1) × 5 = 79. Move the 4 across to get (n - 1) × 5 = 75, divide by 5 to get n - 1 = 15, and add 1: n = 16. So 79 is the 16th term.
The answer has to be a whole number, 1 or more, because positions are 1st, 2nd, 3rd and so on. If n comes out as 15.4, or as 0 or below, the number is not in the sequence at all.
Challenge
The sequence 5, 8, 11, ... has the rule a(n) = 5 + (n - 1) × 3. The board asks which term equals 101. Solve for n.
Try it yourself
Solve for n
Test yourselfThis lesson includes a short quiz. Start the lesson to answer it and track your progress.
All lessons in Exponentials, Logs & Sequences
1Exponential Functions
Repeated MultiplyingGrowth or DecayDrawing GrowthDrawing DecayRecap: Exponential Functions