Big Ideas Math Integrated I, 2016
BI
Big Ideas Math Integrated I, 2016 View details
6. Arithemetic Sequences
Continue to next subchapter

Exercise 40 Page 205

What is the equation for the n^(th) term of an arithmetic sequence?

Error: The formula used is incorrect.
Correct Equation: a_n=6+8n

Practice makes perfect

First we will write the equation of the sequence ourselves. Then we will identify the error.

Writing the Equation

We have been given the following arithmetic sequence.

The arithmetic sequence 14, 22, 30, 38...

We want to write an equation for the n^(th) term of this sequence. Let's recall the equation for an arithmetic sequence. a_n= a_1+(n-1) d Here, a_1 represents the first term of the sequence and d represents the common difference. Let's identify these in our sequence.

The arithmetic sequence 14, 22, 30, 38... with the common difference marked between each term.
The first term is 14 and the common difference is 8. By substituting these values into the explicit rule and simplifying the expression we find the equation for the n^(th) term.
a_n=a_1+(n-1)d
a_n= 14+(n-1) 8
a_n=14+8n-8
a_n=6+8n

Identifying the Error

We can see that when writing the explicit rule, an incorrect formula was used. The correct one is that the n^(th) term equals the sum of the first term and the product of (n-1) and the common difference. a_n= a_1+(n-1) d