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Date November 2016 Marks available 2 Reference code 16N.3srg.hl.TZ0.1
Level HL only Paper Paper 3 Sets, relations and groups Time zone TZ0
Command term Write Question number 1 Adapted from N/A

Question

Let \(\{ G,{\text{ }} \circ \} \) be the group of all permutations of \(1,{\text{ }}2,{\text{ }}3,{\text{ }}4,{\text{ }}5,{\text{ }}6\) under the operation of composition of permutations.

Consider the following Venn diagram, where \(A = \{ 1,{\text{ }}2,{\text{ }}3,{\text{ }}4\} ,{\text{ }}B = \{ 3,{\text{ }}4,{\text{ }}5,{\text{ }}6\} \).

N16/5/MATHL/HP3/ENG/TZ0/SG/01.f

(i)     Write the permutation \(\alpha = \left( {\begin{array}{*{20}{c}} 1&2&3&4&5&6 \\ 3&4&6&2&1&5 \end{array}} \right)\) as a composition of disjoint cycles.

(ii)     State the order of \(\alpha \).

[3]
a.

(i)     Write the permutation \(\beta = \left( {\begin{array}{*{20}{c}} 1&2&3&4&5&6 \\ 6&4&3&5&1&2 \end{array}} \right)\) as a composition of disjoint cycles.

(ii)     State the order of \(\beta \).

[2]
b.

Write the permutation \(\alpha  \circ \beta \) as a composition of disjoint cycles.

[2]
c.

Write the permutation \(\beta  \circ \alpha \) as a composition of disjoint cycles.

[2]
d.

State the order of \(\{ G,{\text{ }} \circ \} \).

[2]
e.

Find the number of permutations in \(\{ G,{\text{ }} \circ \} \) which will result in \(A\), \(B\) and \(A \cap B\) remaining unchanged.

[2]
f.

Markscheme

(i)     \((1{\text{ }}3{\text{ }}6{\text{ }}5)(2{\text{ }}4)\)     A1A1

(ii)     4     A1

 

Note: In (b) (c) and (d) single cycles can be omitted.

 

[3 marks]

a.

(i)     \((1{\text{ }}6{\text{ }}2{\text{ }}4{\text{ }}5)(3)\)     A1

(ii)     5     A1

[2 marks]

b.

\(\left( {\begin{array}{*{20}{c}} 1&2&3&4&5&6 \\ 5&2&6&1&3&4 \end{array}} \right) = (1{\text{ }}5{\text{ }}3{\text{ }}6{\text{ }}4)(2)\)    (M1)A1

[2 marks]

c.

\(\left( {\begin{array}{*{20}{c}} 1&2&3&4&5&6 \\ 3&5&2&4&6&1 \end{array}} \right) = (1{\text{ }}3{\text{ }}2{\text{ }}5{\text{ }}6)(4)\)    (M1)A1

 

Note: Award A2A0 for (c) and (d) combined, if answers are the wrong way round.

 

[2 marks]

d.

\(6! = 720\)    A2

[2 marks]

e.

any composition of the cycles (1 2), (3 4) and (5 6)     (M1)

so \({2^3} = 8\)     A1

[2 marks]

f.

Examiners report

[N/A]
a.
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b.
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c.
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d.
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e.
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f.

Syllabus sections

Topic 8 - Option: Sets, relations and groups » 8.10 » Permutations under composition of permutations.

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