NAME
10-2
DATE
PERIOD
Study Guide and Intervention
Arithmetic Sequences and Series
Arithmetic Sequences
Definition
d = an + 1 - an
The common difference in an
arithmetic sequence with consecutive
terms … 5, 7, … is
7 - 5 = 2.
an = a1 + (n - 1) d where a1 is the
common difference and n is any
positive integer.
The fifth term of the arithmetic
sequence with first term 3 and
common difference 2 is
3 + (4 × 2) = 11.
Common Difference
nth Term of an Arithmetic
Sequence
Example
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
Find the thirteenth term of the arithmetic sequence with a1 = 21
Example 1
and d = - 6.
Use the formula for the nth term of an arithmetic sequence with a1 = 21, n = 13, and
d = – 6.
an = a1 + (n - 1) d
Formula for the nth term
a13 = 21 + (13 – 1) (-6)
n = 13, a1 = 21, d = - 6
a13 = -51
Example 2
Write an equation for the nth term of the arithmetic sequence
-14, -5, 4, 13, … .
In this sequence, a1 = -14 and d = 9.
Use the formula for an to write an equation.
an = a1 + (n - 1) d
Formula for the nth term
an = –14 + (n - 1)(9)
a1 = -14, d = 9
an = –14 + 9n - 9
Distributive Property
an = 9n - 23
Simplify.
Exercises
Find the indicated term of each arithmetic sequence.
1. Find the twentieth term of the arithmetic sequence with a1 = 15 and d = 4.
2. Find the seventh term of the arithmetic sequence with a1 = -81 and d = 12.
3. Find the eleventh term of the arithmetic sequence with a1 = 42 and d = – 5.
4. Find a31 of the arithmetic sequence 18, 15, 12, 9, ….
5. Find a100 of the arithmetic sequence -63, -58, -53, -48, ....
Write an equation for the nth term of each arithmetic sequence.
6. a1 = 15 and d = 38
7. a1 = 72 and d = -13
8. -56, -39, -22, -5, …
9. -94, -52, -10, 32, …
10. 63, 70, 77, 84, …
Chapter 10
11
Glencoe Algebra 2
Lesson 10-2
Term
NAME
10-2
DATE
PERIOD
Study Guide and Intervention
(continued)
Arithmetic Sequences and Series
Arithmetic Series
A shorthand notation for representing a series makes use of the
5
Greek letter Σ. The sigma notation for the series 6 + 12 + 18 + 24 + 30 is ∑ 6n.
n=1
Partial Sum of an
Arithmetic Series
The sum Sn of the first n terms of an arithmetic series is given by the formula
n
n [2a + (n - 1)d ] or S = −
Sn = −
(a1 + an).
1
n
2
2
Example 2
Example 1
Find Sn for the
arithmetic series with a1 = 14,
an = 101, and n = 30.
k=1
Use the sum formula for an arithmetic
series.
n
(a1 + an)
Sum formula
Sn = −
S30
18
Evaluate ∑ (3k + 4).
2
30
= − (14 + 101) n = 30, a1 = 14, an = 101
2
= 15(115)
Simplify.
= 1725
Multiply.
The sum of the series is 1725.
The sum is an arithmetic series with common
difference 3. Substituting k = 1 and k = 18 into
the expression 3k + 4 gives a1 = 3(1) + 4 = 7
and a18 = 3(18) + 4 = 58. There are
18 terms in the series, so n = 18. Use the
formula for the sum of an arithmetic series.
n
Sn = −
(a1 + an)
Sum formula
S18
2
18
= − (7 + 58)
2
= 9(65)
= 585
n = 18, a1 = 7, an = 58
Simplify.
Multiply.
18
So ∑ (3k + 4) = 585.
k=1
Find the sum of each arithmetic series.
1. a1 = 12, an = 100,
n = 12
2. a1 = 50, an = -50,
n = 15
3. a1 = 60, an = -136,
n = 50
4. a1 = 20, d = 4,
an = 112
5. a1 = 180, d = -8,
an = 68
6. a1 = -8, d = -7,
an = -71
7. a1 = 42, n = 8, d = 6
1
8. a1 = 4, n = 20, d = 2 −
2
10. 8 + 6 + 4 + … + -10
42
12. ∑ (4n - 9)
n = 18
Chapter 10
9. a1 = 32, n = 27, d = 3
11. 16 + 22 + 28 + … + 112
50
44
13. ∑ (3n + 4)
14. ∑ (7j - 3)
j=5
n = 20
12
Glencoe Algebra 2
Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
Exercises