3-6 Arithmetic Sequences Warm Up Lesson Presentation Lesson Quiz Holt Algebra 1 Warm Up Lesson Presentation Lesson Quiz Holt McDougal Algebra 1

Objectives Recognize and extend an arithmetic sequence. Find a given term of an arithmetic sequence.

Example 1A: Identifying Arithmetic Sequences Determine whether the sequence appears to be an arithmetic sequence. If so, find the common difference and the next three terms. 9, 13, 17, 21,… Step 1 Find the difference between successive terms. 9, 13, 17, 21,… You add 4 to each term to find the next term. The common difference is 4. +4

Example 1A Continued Determine whether the sequence appears to be an arithmetic sequence. If so, find the common difference and the next three terms. 9, 13, 17, 21,… Step 2 Use the common difference to find the next 3 terms. 9, 13, 17, 21, 25, 29, 33,… an = an-1 + d +4 The sequence appears to be an arithmetic sequence with a common difference of 4. The next three terms are 25, 29, 33.

Example 1B: Identifying Arithmetic Sequences Determine whether the sequence appears to be an arithmetic sequence. If so, find the common difference and the next three terms. 10, 8, 5, 1,… Find the difference between successive terms. 10, 8, 5, 1,… The difference between successive terms is not the same. –2 –3 –4 This sequence is not an arithmetic sequence.

Check It Out! Example 1b Determine whether the sequence appears to be an arithmetic sequence. If so, find the common difference and the next three terms. –4, –2, 1, 5,… Step 1 Find the difference between successive terms. –4, –2, 1, 5,… The difference between successive terms is not the same. +2 +3 +4 This sequence is not an arithmetic sequence.

Example 2A: Finding the nth Term of an Arithmetic Sequence Find the indicated term of the arithmetic sequence. 16th term: 4, 8, 12, 16, … Step 1 Find the common difference. 4, 8, 12, 16,… The common difference is 4. +4 +4 +4 Step 2 Write a rule to find the 16th term. an = a1 + (n – 1)d Write a rule to find the nth term. a16 = 4 + (16 – 1)(4) Substitute 4 for a1,16 for n, and 4 for d. = 4 + (15)(4) Simplify the expression in parentheses. = 4 + 60 Multiply. The 16th term is 64. = 64 Add.

Check It Out! Example 2a Find the indicated term of the arithmetic sequence. 60th term: 11, 5, –1, –7, … Step 1 Find the common difference. 11, 5, –1, –7,… The common difference is –6. –6 –6 –6 Step 2 Write a rule to find the 60th term. an = a1 + (n – 1)d Write a rule to find the nth term. Substitute 11 for a1, 60 for n, and –6 for d. a60 = 11 + (60 – 1)(–6) +2 = 11 + (59)(–6) Simplify the expression in parentheses. = 11 + (–354) Multiply. = –343 Add. The 60th term is –343.