Warm up1.

2.

3.

2x-5 -3x+25 =125

x-72x+1 1

4 =64

-3-8 23x y z

Questions over HW?

Geometric Sequence

A sequence of terms that have a common ratio between them

Explicit Formula

Formula used to find the nth term of a sequence

Explicit Formula for Geometric

Sequence

1

1

n

na a r

Where a1 is the first term in the sequence and

r is the common ratio

Geometric Sequence

Example 1: Find the common ratio

r = 2

4 8 16 32, , , ,...2

1

If you get stuck,

try aa

Geometric Sequence

Example 2 : Find the common ratio 256, 64, 16, 4, …

r = 1/4

64256

r

Example 3: Find the common ratio, the explicit formula, and the seventh term. 6, 3, 1.5, 0.75 …

1

1

n

na a r

11

62

n

na

7 1

7 6 0.5a

3 1

.56 2

r or

7 0.094a

Example 4: Find the common ratio, the explicit formula, and the tenth term. -4, -12, -36, -108 …

1

1

n

na a r

14 3

n

na

10 1

10 4 3a

12

34

r

10 78,732a

Example 5 : The fifth term is 1,792. The common ratio is 4. Write the explicit formula.

5 1792 and 5 and 4a n r

17 4

n

na

5 1

11792 4a

1

1

n

na a r

17 a

Example 6 : During the month of October, a few teachers decided to spread some holiday fun by starting a game of getting “boo”ed. On the first day, 3 teachers were given “boo” bags and directions to “boo” 2 other teachers. If every teacher followed the directions to “boo” 2 teachers with candy and a sign, find the following:

a. The explicit formula b. The first 4 terms

1

1

n

na a r

1a r

13 2

n

na

3, 6, 12, 24…

3 2

HomeworkHomework

Sequence Practice WS