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VCE 11 General 2023

5.05 Geometric sequences

Worksheet
Geometric sequences
1

Explain how the common ratio of a geometric sequence can be found.

2

Find the common ratio of the following geometric sequences:

a

2, - 16, 128, - 1024, \ldots

b

- 9, 8.1, - 7.29, 6.561,\ldots

c

- 70.4, - 17.6, - 4.4, - 1.1, \ldots

3

Write down the next two terms for the following sequences:

a

4, 12, 36, \ldots

b

12, -48, 192, \ldots

c

1, \dfrac {3}{4}, \dfrac {9}{16}, \ldots

d

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

4

Write down the next three terms for the following sequences:

a
- 1, 8, -64, \ldots
b
-1, - 7, - 49, \ldots
5

Consider the first four terms in this geometric sequence: - 8, - 16, - 32, - 64,\ldots

a

Evaluate:

i

\dfrac {T_2}{T_1}

ii

\dfrac {T_3}{T_2}

iii

\dfrac {T_4}{T_3}

b

Hence, find the value of T_5.

6

For each of the following, write the first four terms in the geometric progression:

a

The first term is 6 and the common ratio is 4.

b

The first term is 7 and the common ratio is - 2.

c

The first term is 700\,000 and the common ratio is 1.04.

d

The first term is - 2 and the common ratio is 3.

e

The first term is 1.3 and the common ratio is - 4.

7

Consider the sequence: 4, - 28, 224, - 1372, \ldots

Is the sequence arithmetic, geometric or neither?

8

For each of the following:

i

Determine if the sequence is arithmetic or geometric. Explain your answer.

ii

Find the common ratio or common difference, whichever is applicable.

a

11, - 99, 891,- 8019, \ldots

b

2, 6, 10, 14, \ldots

9

Find the missing terms in the following geometric progressions:

a

- 5, x, - 80, 320, y

b

a, b, \dfrac {3}{25}, - \dfrac {3}{125}, c

10

State whether each of the following sequences is a geometric progression:

a

4, - 4, 4, - 4, \ldots

b

1, \sqrt{6}, 6, 6 \sqrt{6},\ldots

c

2, 0, - 2, - 4,\ldots

d

2, 2^{2}, 2^{4}, 2^{6}, \ldots

11

Suppose t_{1}, t_{2}, t_{3}, t_{4}, t_{5},\ldots is a geometric sequence.

Is t_{1}, t_{3}, t_{5},\ldots also a geometric sequence? Explain your answer.

12

For each of the given explicit rules:

i

List the first four terms of the sequence.

ii

State the common ratio.

a

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

b

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

13

For the following geometric sequences:

i

State the general or explicit rule for the nth term of the sequence.

ii

Find T_{10}.

a
- 2, - 12, - 72, - 432,\ldots
b
- 0.3, - 1.5, - 7.5, - 37.5, \ldots
14

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

15

If the first term of a sequence is 1.2 and the common ratio is - 5, find the 4th term.

16

If the first term of a sequence is 400\,000 and the common ratio is 1.12, find the 3rd term.

17

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

Find the first three terms of the geometric progression.

18

In a geometric progression, T_4 = 32 and T_6 = 128.

a

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

b

For the case where r is postive, find the value of a, the first term in the sequence.

c

Consider the sequence in which the first term is positive.

Find an expression for T_n, the nth term of this sequence.

19

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

20

Find three consecutive positive terms of a geometric progression if they have a product of 125 and the third term is 9 times the first.

21

Consider the finite sequence: 4, 4 \sqrt{2}, 8, \ldots, 256

a

Find the common ratio.

b

Find T_6.

c

Solve for n, the number of terms in the sequence.

22

Find the common ratio for the geometric sequence where the first two terms are \sqrt{5} + \sqrt{3} and \sqrt{5} - \sqrt{3}.

23

Consider the following:

a

1, x and y are the first three terms of an arithmetic sequence. Form an equation for y in terms of x.

b

1, y and x are also the first three terms in a geometric sequence. Form an equation for x in terms of y.

c

Hence, solve for the values of y.

d

One solution is y = 1 and x = 1 which produces the sequence 1, 1, 1.

i

Find the first three values of the arithmetic sequence for the other solution for x and y, along with the common difference.

ii

Find the first three values of the geometric sequence for the other solution for x and y, along with the common ratio.

Geometric sequences in tables and graphs
24

Consider the recurrence relation: u_{n + 1} = 2 u_n, u_1=4.

a

Complete the table of values:

b

Find u_7.

n1234
u_n4
25

The nth term of a geometric progression is given by the equation T_n = 25 \times \left(\dfrac {1}{5}\right)^{n - 1}.

a

Complete the table of values:

b

Find the common ratio.

n123410
T_n
26

The nth term of a geometric progression is given by the equation T_n = - 72 \times \left( - \dfrac {4}{3} \right)^{n - 1}.

a

Complete the table of values:

b

Find the common ratio.

n12346
T_n
27

Each of the given tables of values represents terms in a geometric sequence:

i

Find r, the common ratio between consecutive terms.

ii

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

iii

Find the missing term in the table.

a
n123410
T_n5403202560
b
n123412
T_n7-2163-189
c
n136911
T_n-5-45-1215-32\,805
d
n12347
T_n-2-\dfrac {16}{3}-\dfrac {128}{9}-\dfrac {1024}{27}
28

The values in the table show the nth term in a geometric sequence for consecutive values of n. Complete the missing values in the table:

a
n12345
T_n5-320
b
n12345
T_n-27-64
29

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

a

Find r, the common ratio between consecutive terms.

b

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

n149
T_n-9576-589\,824
30

The nth term of a geometric progression is given by the equation T_n = 2 \times 3^{n - 1}

a

Complete the table of values:

b

Find the common ratio between consecutive terms.

n123410
T_n
c

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

d

State whether the joined points would form a straight line or a curve.

31

The nth term of a geometric progression is given by the equation T_n = 6 \times \left( - 2 \right)^{n - 1}

a

Complete the table of values:

b

Find the common ratio between consecutive terms.

n123411
T_n
c

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

d

Describe the shape of the joined points.

32

The plotted points represent terms in a geometric sequence:

a

Find the first term in the sequence.

b

Identify r, the common ratio between consecutive terms.

c

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

1
2
3
4
n
-18
-16
-14
-12
-10
-8
-6
-4
-2
T_n
33

The plotted points represent terms in a geometric sequence:

a

Complete the table of values for the given points:

n1234
T_n
b

Identify r, the common ratio between consecutive terms.

c

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

d

Find the 10th term of the sequence.

1
2
3
4
5
n
2
4
6
8
10
12
14
16
18
20
22
24
T_n
34

The plotted points represent terms in a geometric sequence:

a

Complete the table of values for the given points:

n123
T_n
b

Identify r, the common ratio between consecutive terms. Assume all values in the series are negative.

c

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

1
2
3
4
5
n
-20
-18
-16
-14
-12
-10
-8
-6
-4
-2
T_n
35

The plotted points represent terms in a geometric sequence:

a

Complete the table of values for the given points.

n123
T_n
b

Identify r, the common ratio between consecutive terms.

c

Find the 4th term of the sequence.

d

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

e

Find the 10th term of the sequence.

1
2
3
4
5
n
-6
-4
-2
2
4
6
8
10
12
14
16
18
T_n
36

The plotted points represent terms in a geometric sequence:

a

Identify r, the common ratio between consecutive terms.

b

Write a simplified expression for the 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
2
4
6
8
10
12
T_n
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Outcomes

U1.AoS2.7

use a given recurrence relation to generate a sequence, deduce the explicit rule, n u from the recursion relation, tabulate, graph and evaluate the sequence

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