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Date November 2015 Marks available 1 Reference code 15N.3srg.hl.TZ0.3
Level HL only Paper Paper 3 Sets, relations and groups Time zone TZ0
Command term State Question number 3 Adapted from N/A

Question

The set of all permutations of the elements 1, 2, 101, 2, 10 is denoted by HH and the binary operation represents the composition of permutations.

The permutation p=(1 2 3 4 5 6)(7 8 9 10)p=(1 2 3 4 5 6)(7 8 9 10) generates the subgroup {G, }{G, } of the group {H, }{H, }.

Find the order of {G, }{G, }.

[2]
a.

State the identity element in {G, }{G, }.

[1]
b.

Find

(i)     pppp;

(ii)     the inverse of pppp.

[4]
c.

(i)     Find the maximum possible order of an element in {H, }{H, }.

(ii)     Give an example of an element with this order.

[3]
d.

Markscheme

the order of (G, )(G, ) is lcm(6, 4)lcm(6, 4)     (M1)

=12=12     A1

[2 marks]

a.

(1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(1)(2)(3)(4)(5)(6)(7)(8)(9)(10)     A1

 

Note:     Accept ( ) or a word description.

[1 mark]

b.

(i)     pp=(1 3 5)(2 4 6)(7 9)(810)pp=(1 3 5)(2 4 6)(7 9)(810)     (M1)A1

(ii)     its inverse =(1 5 3)(2 6 4)(7 9)(810)=(1 5 3)(2 6 4)(7 9)(810)     A1A1

 

Note:     Award A1 for cycles of 2, A1 for cycles of 3.

[4 marks]

c.

(i)     considering LCM of length of cycles with length 2233 and 55     (M1)

3030     A1

(ii)     eg(1 2)(3 4 5)(6 7 8 9 10)(1 2)(3 4 5)(6 7 8 9 10)     A1

 

Note:     allow FT as long as the length of cycles adds to 1010 and their LCM is consistent with answer to part (i).

 

Note: Accept alternative notation for each part

[3 marks]

Total [10 marks]

d.

Examiners report

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

Syllabus sections

Topic 8 - Option: Sets, relations and groups » 8.6 » The identity element ee.

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