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Terms of Arithmetic Sequences. 13-1. Course 3. Warm Up Find the next two numbers in the pattern, using the simplest rule you can find. 1. 1, 5, 9, 13, . . . 2. 100, 50, 25, 12.5, . . . 3. 80, 87, 94, 101, . . . 4. 3, 9, 7, 13, 11, . . . 17, 21. 6.25, 3.125. 108, 115. 17, 15.
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Terms of Arithmetic Sequences 13-1 Course 3 Warm Up Find the next two numbers in the pattern, using the simplest rule you can find. 1.1, 5, 9, 13, . . . 2. 100, 50, 25, 12.5, . . . 3. 80, 87, 94, 101, . . . 4. 3, 9, 7, 13, 11, . . . 17, 21 6.25, 3.125 108, 115 17, 15
Caution! You cannot tell if a sequence is arithmetic by looking at a finite number of terms because the next term might not fit the pattern.
Additional Example 1A: Identifying Arithmetic Sequences Determine if the sequence could be arithmetic. If so, give the common difference. 5, 8, 11, 14, 17, . . . The terms increase by 3. 5 8 11 14 17, . . . 3 3 3 3 The sequence could be arithmetic with a common difference of 3.
Additional Example 1B: Identifying Arithmetic Sequences Determine if the sequence could be arithmetic. If so, give the common difference. 1, 3, 6, 10, 15, . . . Find the difference of each term and the term before it. 1 3 6 10 15, . . . 5 4 2 3 The sequence is not arithmetic.
Additional Example 1C: Identifying Arithmetic Sequences Determine if the sequence could be arithmetic. If so, give the common difference. 65, 60, 55, 50, 45, . . . The terms decrease by 5. 65 60 55 50 45, . . . –5 –5 –5 –5 The sequence could be arithmetic with a common difference of –5.
Additional Example 1D: Identifying Arithmetic Sequences Determine if the sequence could be arithmetic. If so, give the common difference. 5.7, 5.8, 5.9, 6, 6.1, . . . The terms increase by 0.1. 5.7 5.8 5.9 6 6.1, . . . 0.1 0.1 0.1 0.1 The sequence could be arithmetic with a common difference of 0.1.
Additional Example 1E: Identifying Arithmetic Sequences Determine if the sequence could be arithmetic. If so, give the common difference. 1, 0, -1, 0, 1, . . . Find the difference of each term and the term before it. 1 0 –1 0 1, . . . 1 1 –1 –1 The sequence is not arithmetic.
Check It Out: Example 1A Determine if the sequence could be arithmetic. If so, give the common difference. 1, 2, 3, 4, 5, . . . The terms increase by 1. 1 2 3 4 5, . . . 1 1 1 1 The sequence could be arithmetic with a common difference of 1.
Check It Out: Example 1B Determine if the sequence could be arithmetic. If so, give the common difference. 1, 3, 7, 8, 12, … Find the difference of each term and the term before it. 1 3 7 8 12, . . . 4 1 2 4 The sequence is not arithmetic.
Check It Out: Example 1C Determine if the sequence could be arithmetic. If so, give the common difference. 11, 22, 33, 44, 55, . . . The terms increase by 11. 11 22 33 44 55, . . . 11 11 11 11 The sequence could be arithmetic with a common difference of 11.
Check It Out: Example 1D Determine if the sequence could be arithmetic. If so, give the common difference. 1, 1, 1, 1, 1, 1, . . . Find the difference of each term and the term before it. 1 1 1 1 1, . . . 0 0 0 0 The sequence could be arithmetic with a common difference of 0.
Check It Out: Example 1E Determine if the sequence could be arithmetic. If so, give the common difference. 2, 4, 6, 8, 9, . . . Find the difference of each term and the term before it. 2 4 6 8 9, . . . 1 2 2 2 The sequence is not arithmetic.
Helpful Hint Subscripts are used to show the positions of terms in the sequence. The first term is a1, “read a sub one,” the second is a2, and so on.
Additional Example 2A: Finding a Given Term of an Arithmetic Sequence Find the given term in the arithmetic sequence. 10th term: 1, 3, 5, 7, . . . an = a1 + (n – 1)d a10 = 1 + (10 – 1)2 a10 = 19
Additional Example 2B: Finding a Given Term of an Arithmetic Sequence Find the given term in the arithmetic sequence. 18th term: 100, 93, 86, 79, . . . an = a1 + (n – 1)d a18 = 100 + (18 – 1)(–7) a18 = -19
Additional Example 2C: Finding a Given Term of an Arithmetic Sequence Find the given term in the arithmetic sequence. 21st term: 25, 25.5, 26, 26.5, . . . an = a1 + (n – 1)d a21 = 25 + (21 – 1)(0.5) a21 = 35
Additional Example 2D: Finding a Given Term of an Arithmetic Sequence Find the given term in the arithmetic sequence. 14th term: a1 = 13, d = 5 an = a1 + (n – 1)d a14 = 13 + (14 – 1)5 a14 = 78
Using Arithmetic Sequence Formula to write a linear equation. Find the value of y when x = 1: -2 Find the common difference: -4 Use an = a1 + (n – 1)d: rewrite an = y, a1 = value of y when x = 1, n = x y =-2 + (x – 1)(-4) = -2 – 4x + 5 Simplify: y = -4x + 2