topic badge

3.06 Geometric progressions -calculator assumed

Worksheet
Geometric progressions
1

For each of the following geometric sequences, evaluate:

i

\dfrac{T_2}{T_1}

ii

\dfrac{T_3}{T_2}

iii

\dfrac{T_4}{T_3}

iv

T_5

a

- 9 , - 10.8 , - 12.96 , - 15.552 , \ldots

b

- 8, -16, -32, -64, \ldots

2

Write down the next two terms in the following sequences:

a

4, 12, 36, \ldots

b

12, -48, 192, \ldots

c

- 6, 9, - \dfrac{27}{2}, \ldots

3

Consider the sequence -1, -7, -49, \ldots

a

Find the next term of the sequence.

b

Find the 5th term of the sequence.

c

Find the 6th term of the sequence.

4

Determine the common ratio of the following geometric sequences:

a

2, - 16, 128, - 1024, ...

b

- 70.4,- 17.6,- 4.4,- 1.1,...

5

Write the first 5 terms of the following sequences given the first term and the common ratio:

a

First term: - 2, common ratio: 3

b

First term: 1.3, common ratio: - 4.

c

First term: 700\,000, common ratio: 1.04.

6

The first term of a sequence is 3.9 and the common ratio is 2.

a

State the 5th term.

b

Calculate the sum of the first 5 terms.

7

Find the missing terms in the geometric sequence below:

x, \dfrac{3}{25}, - \dfrac{3}{125}, y, \ldots

8

If t_{1}, t_{2}, t_{3}, t_{4}, t_{5}, \text{. . .} is a geometric sequence, is t_{1}, t_{3}, t_{5}, \text{. . .} a geometric sequence?

9

In a geometric progression, T_7 = \dfrac{64}{81} and T_8 = \dfrac{128}{243}.

a

Find the value of r, the common ratio in the sequence.

b

List the first three terms of the geometric progression.

Recursive rule
10

For each of the following sequences, write the recursive rule for T_n in terms of T_{n-1} including the initial term T_1:

a

9, 45, 225, 1125, \ldots

b

2, 20, 200, 2000, \ldots

c

5, - 15 , 45, - 135 , \ldots

11

List the first 5 terms of the following sequences defined by:

a

a_1 = 2 and a_{n+1} = 3 a_n

b

a_1 = 8 and a_n = \dfrac{1}{2} a_{n - 1}

12

The first term of a geometric sequence is 7, and the fourth term is 875.

a

Find the common ratio, r, of this sequence.

b

Write the recursive rule for T_{n+1} in terms of T_n, including the initial term T_1.

c

Calculate the sum of the terms between the 4th and 9th term inclusive.

13

The first term of a geometric sequence is 6, and the third term is 96.

a

Find the possible values of the common ratio, r, of this sequence.

b

Write the recursive rule for T_n in terms of T_{n - 1} that uses the positive common ratio, and the initial term T_1.

c

Write the recursive rule for S_n in terms of S_{n - 1} that uses the positive common ratio, and the initial term S_1.

d

Determine the sum of the terms between T_4 and T_8 inclusive.

14

The fourth term of a geometric sequence is 16, and the seventh term is 128.

a

Find the common ratio, r, of this sequence.

b

Find the first term of this sequence.

c

Write the recursive rule for T_{n+1} in terms of T_n, including the initial term T_1.

d

Determine the sum of the terms between the 3rd and 10th term inclusive.

15

The third term of a geometric sequence is 7500, and the seventh term is 12.

a

Find the common ratio, r, of this sequence.

b

Find the first term of this sequence.

c

Write the recursive rule for T_n in terms of T_{n - 1} that uses the positive common ratio, and the initial term T_1.

d

Write the recursive rule for S_n in terms of S_{n - 1} that uses the positive common ratio, and the initial term S_1.

e

Calculate the sum of the first 15 terms of the sequence containing a negative common ratio. Round your answer to the nearest whole number.

16

Consider the following sequence:

3000, 600, 120, 24, \ldots

a

Write the recursive rule for T_{n+1} in terms of T_n , including the initial term T_1.

b

Determine the sum of the first 10 terms. Round your answer to the nearest whole number.

17

If the first term of a sequence is 90\,000 and the common ratio is 1.11:

a

Find the 6th term. Round your answer to three decimal places.

b

Calculate the sum of the first 6 terms. Round your answer to the nearest whole number.

Explicit rule
18

Given the nth term of the following sequences defined by the given equation:

i

Write the first four terms of the sequence.

ii

Find the common ratio.

a

T_n = 3 \times 4^{n - 1}

b

T_n = - 4 \times \left( - 3 \right)^{n - 1}

19

Consider the following sequence:

- 54 , - 18 , - 6 , - 2 , \ldots

a

Write the general rule for T_n, the nth term of the sequence.

b

Hence, state the next three terms of the sequence.

c

Find T_9, the 9th term of the sequence.

d

Calculate the sum of the first 9 terms. Round your answer to the nearest whole number.

20

If the first term of a sequence is 27 and the common ratio is \dfrac{1}{3}, find the 10th term.

21

Consider the following sequence:

- 0.3,- 1.5,- 7.5,- 37.5,...

a

Find the formula for the nth term of the sequence.

b

Hence, find the next three terms of the sequence.

22

In a geometric progression, T_4 = - 192 and T_7 = 12\,288.

a

Determine the value of r

b

Hence determine the value of a

c

Write an expression for T_n

23

In a geometric progression, T_4 = 192 and T_9 = 196\,608.

a

Find the value of r.

b

Hence determine the value of a.

c

Write an expression for T_n.

24

Insert three positive values between 18 and \dfrac{32}{9} such that the five terms form the successive terms in a geometric progression.

25

Three consecutive positive terms of a geometric progression have a product of 125. The third term is 9 times the first. Let the common ratio be r, and the middle term be b.

a

Find the the value of b.

b

Find the three consecutive terms.

c

State the value of r.

Geometric sequences in tables and graphs
26

Consider the first-order recurrence relationship defined by T_n = 2 T_{n - 1},\text{ } T_1 = 2.

a

Determine the next three terms of the sequence from T_2 to T_4.

b

Plot the first four terms on a number plane.

c

Is the sequence arithmetic or geometric?

27

Consider the following sequence 5, - 10 , 20, - 40 , \ldots

a

Plot the first four terms on a cartesian plane.

b

Is the sequence arithmetic or geometric?

28

Consider the sequence plot drawn below:

a

State the terms of the first five points of the sequence.

b

Is the sequence arithmetic or geometric?

c

Write a recursive rule for T_{n+1} in terms of T_n and an initial condition for T_1.

1
2
3
4
5
n
2
4
6
8
10
12
14
16
18
20
T_n
29

Consider the sequence 54, 18, 6, 2, \ldots

a

If the sequence starts from n = 1, plot the first four terms on a number plane.

b

Is the relationship depicted by this graph linear, exponential or neither?

c

Write the recursive rule for T_{n+1} in terms of T_n, including the initial term T_1.

d

Find the sum of the first 10 terms. Round your answer to the nearest whole number.

30

Consider the sequence plot drawn below:

a

State the terms of the first five terms of the sequence.

b

Is the relationship depicted by this graph linear, exponential or neither?

c

Write the recursive rule for T_n in terms of T_{n - 1}, including the initial term T_1.

d

Calculate the sum of the first 12 terms. Round your answer to the nearest whole number.

1
2
3
4
5
n
-8
-6
-4
-2
2
4
6
8
10
12
14
16
T_n
31

Given the nth term of the following geometric progressions:

i

Complete the table of values.

ii

Find the common ratio.

iii

Plot the points in the table that correspond to n = 1, n = 2, n = 3 and n = 4 on a cartesian plane.

iv

State whether the joined points would form a straight line, a wave shaped curve, a parabola, or an exponential curve.

a

T_n = 2 \times 3^{n - 1}.

n123410
T_n
b

T_n = 6 \times \left( - 2 \right)^{n - 1}.

n123411
T_n
32

For the geometric progressions given by the equations below:

i

Complete the table of values.

ii

Find the common ratio.

a

T_n = 25 \times \left(\dfrac{1}{5}\right)^{n - 1}

n123410
T_n
b

T_n = - 72 \times \left( - \dfrac{4}{3} \right)^{n - 1}.

n12346
T_n
33

For the geometric sequences given by the tables of values below:

i

Determine the common ratio, r.

ii

Write an expression for the general nth term of the sequence, T_n.

iii

Find the missing value in the table.

a
n123410
T_n5403202560
b
n123412
T_n7-2163-189
c
n12347
T_n-2-\dfrac{16}{3}-\dfrac{128}{9}-\dfrac{1024}{27}
d
n136911
T_n-5-45-1215-32\,805
34

The given table of values represents terms in a geometric sequence:

a

Find r, the common ratio.

b

Write an expression for the general nth term of the sequence, T_n.

n149
T_n-9576-589\,824
35

For the following geometric sequences represented by the plotted points:

i

Complete a table of values for the given points.

ii

Find r, the common ratio.

iii

Write a simplified expression for the general nth term of the sequence, T_n.

iv

Find the 10th term of the sequence.

a
1
2
3
4
5
n
5
10
15
20
25
T_n
b
1
2
3
4
5
n
-60
-50
-40
-30
-20
-10
10
20
T_n
36

The plotted points represent terms in a geometric sequence.

a

Complete a table of values for the points.

b

Find r, the common ratio. Assume all values in the series are negative.

c

Write an expression for the general nth term of the sequence, T_n.

1
2
3
n
-18
-16
-14
-12
-10
-8
-6
-4
-2
2
T_n
37

Complete the missing values in the following tables that show the nth term in a geometric sequence:

a
n12345
T_n5-320
b
n12345
T_n-27-64
38

The plotted points represent terms in a geometric sequence:

a

State the first term in the sequence.

b

Find r, the common ratio.

c

Write an expression for the general nth term of the sequence, T_n.

1
2
3
n
-18
-16
-14
-12
-10
-8
-6
-4
-2
T_n
39

The plotted points represent terms in a geometric sequence:

a

Find r, the common ratio.

b

Write an expression for the general nth term of the sequence, T_n.

c

The points are reflected about the horizontal axis to form three new points. If these new points represent consecutive terms of a geometric sequence, write the equation for T_k, the kth term in this new sequence.

1
2
3
4
5
n
1
2
3
4
5
6
7
8
9
10
11
12
13
14
T_n
Sign up to access Worksheet
Get full access to our content with a Mathspace account

Outcomes

3.2.5

use recursion to generate a geometric sequence

3.2.6

display the terms of a geometric sequence in both tabular and graphical form and demonstrate that geometric sequences can be used to model exponential growth and decay in discrete situations

3.2.7

deduce a rule for the nth term of a particular geometric sequence from the pattern of the terms in the sequence, and use this rule to make predictions

What is Mathspace

About Mathspace