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Arithmetic Sequences - PowerPoint PPT Presentation


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Arithmetic Sequences. A sequence in which a constant (d) can be added to each term to get the next term is called an. Arithmetic Sequence. The constant (d) is called the. Definition. Common Difference. To find the common difference (d), subtract any term from one that follows it. t 1. t 2.

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Presentation Transcript
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A sequence in which a constant (d) can be added to each term to get the next term is called an

Arithmetic Sequence.

The constant (d) is called the

Definition

Common Difference.

To find the common difference (d), subtract any term from one that follows it.

t1

t2

t3

t4

t5

2 5 8 11 14

3

3

3

3

slide3

Find the first term and the common difference of each arithmetic sequence.

Examples:

First term (a):

4

Common difference (d):

= 9 – 4 = 5

First term (a):

34

-7

Common difference (d):

BE CAREFUL: ALWAYS CHECK TO MAKE SURE THE DIFFERENCE IS THE SAME BETWEEN EACH TERM !

slide4

Now you try!

Find the first term and the common difference of each of these arithmetic sequences.

a) 1, -4, -9, -14, ….

b) 11, 23, 35, 47, ….

c) 3x-8, x-8, -x-8, -3x-8

d) s-4, 3s-3, 5s-2, 7s-1, …..

slide5

Answers with solutions

a) 1, -4, -9, -14, ….

a = 1 and

d = a2 - a1= - 4 - 1 = - 5

a = 11 and

d = a2 - a1= 23 - 11 = 12

b) 11, 23, 35, 47, ….

a = 3x-8 and

d = a2 - a1= x – 8 – (3x – 8) = - 2x

c) 3x-8, x-8, -x-8, -3x-8

a = s - 4 and

d = a2 - a1= 3s – 3 – (s – 4) = 2s + 1

d) s-4, 3s-3, 5s-2, 7s-1, …..

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The first term of an arithmetic sequence is . We add (d) to get the next term. There is a pattern, therefore there is a formula we can use to give use any term that we need without listing the whole sequence .

The nth term of an arithmetic sequence is given by:

tn = a + (n – 1) d

The last # in the sequence/or the # you are looking for

The position the term is in

First term

The common difference

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You are looking for the term!

Examples:

Find the 14th term of the arithmetic sequence

4, 7, 10, 13,……

tn = a + (n – 1) d

t14 =

The 14th term in this sequence is the number 43!

slide8

Now you try!

Find the 10th and 25th term given the following information. Make sure to derive the general formula first and then list ehat you have been provided.

a) 1, 7, 13, 19 ….

b) x+10, x+7, x+4, x+1, ….

c) The first term is 3 and the common difference is -21

d) The second term is 8 and the common difference is 3

slide9

Answers with solutions

a = 1 and d = a2 - a1= 7 – 1 = 6

tn=a+(n-1)d = 1 + (n-1) 6 = 1+6n-6 = 6n-5

t10 = 6(10) – 5 = 55

t25 = 6(25)-5 = 145

a) 1, 7, 13, 19 …. ….

a = x+10and d = a2 - a1= x+7-(x+10) = -3

tn=a+(n-1)d = x+10 + (n-1)(-3) = x+10-3n+3 = x-3n+13

t10 = x -3(10)+13 = x - 17

t25 = x -3(25)+13 = x - 62

b) x+10, x+7, x+4, x+1,.

a = 3 and d = 21

tn=a+(n-1)d = 3 + (n-1) 21 = 3+21n-21 = 21n-18

t10 = 21(10) – 5 = 205 t25 = 21(25)-5 = 520

c) The first term is 3 and the common difference is -21

d) The second term is 8 and the common difference is 3

a = 8 - 3 = 5 and d = 3

tn=a+(n-1)d = 5 + (n-1) 3 = 5+3n-3 = 3n+2

t10 = 3(10) +2 = 32 t25 = 3(25)+2 = 77

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You are looking for the term! List which variables from the general term are provided!

Examples:

Find the 14th term of the arithmetic sequence with first term of 5 and the common difference is –6.

a = 5 and d = -6

tn = a + (n – 1) d

t14 =

-6

5

= 5 + (13) * -6

= 5 + -78

= -73

The 14th term in this sequence is the number -73!

slide11

You are looking for n!

Examples:

In the arithmetic sequence 4,7,10,13,…, which term has a value of 301?

tn = a + (n – 1) d

The 100th term in this sequence is 301!

slide12

t10=33

t22= -3

Use what you know!

tn = a + (n – 1) d

tn = a + (n – 1) d

For term 22: -3= a + 21d

For term 10: 33= a + 9d

Examples:

In an arithmetic sequence, term 10 is 33 and term 22 is –3. What are the first four terms of the sequence?

HMMM! Two equations you can solve!

SOLVE:

33 = a+9d

-3 = a+21d

By elimination -36 = 12d

-3 = d

SOLVE:

33 = a + 9d

33 = a +9(-3)

33 = a –27

60 = a

The sequence is 60, 57, 54, 51, …….