# Lesson 3: Arithmetic Sequences

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Lesson 3: Arithmetic Sequences
, , , ,
2. How could you describe this pattern so that someone else could draw the sixth term? The 10 th
term?
3. We can also look at this pattern with numbers. How do the figures relate to the sequence 2, 5, 8, ... ?
4. Find the next three terms of the sequence: 2, 5, 8, …
5. Do the values you got in Exercise 4 correspond to the figures you drew in Exercise 1?
Using a recursive formula we can easily see how the pattern is changing, but to answer questions like, “How
many squares would be in the 100 th
term?” is difficult with this type of formula. In Lesson 1 we used some
explicit formulas and found that explicit formulas make questions about the 100 th
term much easier to
answer. In this lesson you’ll learn to write explicit formulas for arithmetic sequences.
Lesson 3: Arithmetic Sequences
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This file derived from ALG I-M3-TE-1.3.0-08.2015
HART INTERACTIVE – ALGEBRA 1 M3 Lesson 3 ALGEBRA I
6. We’ll continue with the same sequence 2, 5, 8, … So 2 is term 1 (n=1), 5 is term 2 (n=2), 8 is term 3 (n=3)
and so forth. Fill in the rest of the table below.
n Term Work Pattern
2 5 2 3 5+ = 2 3(1) 5+ =
3 8 2 3 3 8+ + =
4 11
B. What pattern(s) do you notice in the graph?
Lesson 3: Arithmetic Sequences
S.24
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This file derived from ALG I-M3-TE-1.3.0-08.2015
HART INTERACTIVE – ALGEBRA 1 M3 Lesson 3 ALGEBRA I
In an arithmetic sequence, each term after the first term differs from the preceding term by a constant
amount. The difference between consecutive terms is called the common difference of the sequence.
8. The sequence 2, 5, 8, … is an arithmetic sequence. What is the common difference of this sequence?
9. How can you easily find the common difference for an arithmetic sequence?
10. If the points in Exercise 7 were connected, what would be the slope of the line formed? How does this
relate to the common difference?
11. A. What would the “0 th
” term be? Is there a figure that could be drawn of the 0 th
term? Explain.
term? What would it be?
Although we could find the 15 th
term by adding 3 over and over, it would be easy to make a mistake
somewhere in the calculations. And finding the 101 st
term would be tedious and time-consuming! Instead of
continuing to add on 3 each time, we’ll write an explicit formula for this sequence.
Lesson 3: Arithmetic Sequences
S.25
This work is derived from Eureka Math ™ and licensed by Great Minds. ©2015 Great Minds. eureka-math.org
This file derived from ALG I-M3-TE-1.3.0-08.2015
HART INTERACTIVE – ALGEBRA 1 M3 Lesson 3 ALGEBRA I
The nth term or the general term of an arithmetic sequence is given by the explicit formula
( ) (1) ( 1)f n f d n= + −
where f(1) is the first term of the sequence and d is the common difference
12. A. Write the explicit formula for the sequence 2, 5, 8, …
B. Compare this formula to the pattern in the table in Exercise 6 for the nth term.
C. Find the 15 th
term and the 101 st
term for this sequence.
13. Find the common difference for the arithmetic sequences and then write the explicit formula for each
one.
A. 142, 138, 134, 130, 126, …
B. – 5, –2, 1, 4, 7, …
14. Write the first six terms of arithmetic sequence where (1) 8f = − , 5d = .
Lesson 3: Arithmetic Sequences
S.26
This work is derived from Eureka Math ™ and licensed by Great Minds. ©2015 Great Minds. eureka-math.org
This file derived from ALG I-M3-TE-1.3.0-08.2015
HART INTERACTIVE – ALGEBRA 1 M3 Lesson 3 ALGEBRA I
Lesson Summary
General Term of an Arithmetic Sequence
The nth term (the general term) of an arithmetic sequence with the first term (1)f and
common difference d is
Homework Problem Set 1. Write a formula for the nth
term of the arithmetic sequence 1, 5, 9, 13, ……. Then use the formula to find (20)f .
2. Find the f(8) of the arithmetic sequence when f(1) = 4 and whose common difference is -7.
3. Daniel gets a job with a starting salary of \$70,000 per year with an annual raise of \$3,000. What will
Daniel’s salary be in the 10 th
year? Write an explicit formula and then solve.
Lesson 3: Arithmetic Sequences
S.27
This work is derived from Eureka Math ™ and licensed by Great Minds. ©2015 Great Minds. eureka-math.org
This file derived from ALG I-M3-TE-1.3.0-08.2015
HART INTERACTIVE – ALGEBRA 1 M3 Lesson 3 ALGEBRA I
4. Save-A-Lot Theater ticket prices were originally \$1 each. Prices have risen by 50 cents each year since.
What is the price of a ticket 7 years later? Write an explicit formula and then solve.
5. The graph shows how the cost of a snowboarding trip depends on the number of boarders.
A. Fill in the chart of the data.
B. Write the explicit rule.
C. Draw a line connecting the data points. What is the y-intercept? What is the slope? Write an
equation of the line in slope-intercept form.
D. What do you notice about the answers in Parts B and C? Explain (use m and d in your response).
Lesson 3: Arithmetic Sequences
S.28
This work is derived from Eureka Math ™ and licensed by Great Minds. ©2015 Great Minds. eureka-math.org
This file derived from ALG I-M3-TE-1.3.0-08.2015
HART INTERACTIVE – ALGEBRA 1 M3 Lesson 3 ALGEBRA I
6. Consider the sequence that follows a plus 3 pattern: 4, 7, 10, 13, 16, ….
A. Write a formula for the sequence using the () notation.
B. Does the formula () = 3( − 1) + 4 generate the same sequence? Why might some people prefer
this formula?
C. Graph the terms of the sequence as ordered pairs ,() on the coordinate plane. What do you
notice about the graph?
Lesson 3: Arithmetic Sequences
S.29
This work is derived from Eureka Math ™ and licensed by Great Minds. ©2015 Great Minds. eureka-math.org
This file derived from ALG I-M3-TE-1.3.0-08.2015
HART INTERACTIVE – ALGEBRA 1 M3 Lesson 3 ALGEBRA I
7. Consider a sequence that follows a minus 5 pattern: 30, 25, 20, 15, ….
A. Write a formula for the th term of the sequence. Be sure to specify what value of your formula
starts with.
B. Using the formula, find the 20th term of the sequence.
C. Graph the terms of the sequence as ordered pairs ,() on the coordinate plane.
Lesson 3: Arithmetic Sequences
S.30
This work is derived from Eureka Math ™ and licensed by Great Minds. ©2015 Great Minds. eureka-math.org
This file derived from ALG I-M3-TE-1.3.0-08.2015
HART INTERACTIVE – ALGEBRA 1 M3 Lesson 3 ALGEBRA I
CHALLENGE PROBLEMS
8. Find an explicit form () for each of the following arithmetic sequences (assume is some real number
and is some real number).
a. −34, −22, −10, 2, ...
b. 1 5,
d. , 2 + 1, 3 + 2, 4 + 3, ...
9. Consider the arithmetic sequence 13, 24, 35, .... a. Find an explicit form for the sequence in terms of .
b. Find the 40th term.
c. If the th term is 299, find the value of .
Lesson 3: Arithmetic Sequences
S.31
This work is derived from Eureka Math ™ and licensed by Great Minds. ©2015 Great Minds. eureka-math.org
This file derived from ALG I-M3-TE-1.3.0-08.2015
HART INTERACTIVE – ALGEBRA 1 M3 Lesson 3 ALGEBRA I
10. If −2, , , , 14 forms an arithmetic sequence, find the values of , , and .
11. 3 + , 9 + 3, 13 + 4, ... is an arithmetic sequence for some real number .
a. Find the value of .
b. Find the 10th term of the sequence.
12. Find an explicit form () of the arithmetic sequence where the 2nd term is 25 and the sum of the 3rd
term and 4th term is 86.
13. In the right triangle figure below, the lengths of the sides cm, cm, and cm of the right triangle form
a finite arithmetic sequence. If the perimeter of the triangle is 18 cm, find the values of , , and .

S.32
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