Date | May 2013 | Marks available | 3 | Reference code | 13M.1.hl.TZ0.2 |
Level | HL only | Paper | 1 | Time zone | TZ0 |
Command term | Show that | Question number | 2 | Adapted from | N/A |
Question
G is a group. The elements a,b∈G , satisfy a3=b2=e and ba=a2b , where e is the identity element of G .
Show that (ba)2=e .
Express (bab)−1 in its simplest form.
Given that a≠e ,
(i) show that b≠e ;
(ii) show that G is not Abelian.
Markscheme
EITHER
baba=baa2b M1
=ba3b (A1)
=b2 A1
=e AG
OR
baba=a2bba M1
=a2b2a (A1)
=a3 A1
=e AG
[3 marks]
bab=a2bb (M1)
=a2 (A1)
(bab)−1=a A1
[3 marks]
(i) assume b=e M1
then a=a2 A1
⇒a=e which is a contradiction R1
(ii) if ab=ba M1
then ab=a2b A1
⇒a=e which is a contradiction R1
[6 marks]
Examiners report
This question was started by the majority of candidates, but only successfully completed by a few. Many candidates seemed to be aware of this style of question, but were either unable to make significant progress or manipulated the algebra in a contorted manner and hence lost valuable time. Also a number of candidates made assumptions about commutativity which were not justified. Overall, the level and succinctness of meaningful algebraic manipulation shown by candidates was disappointing.
This question was started by the majority of candidates, but only successfully completed by a few. Many candidates seemed to be aware of this style of question, but were either unable to make significant progress or manipulated the algebra in a contorted manner and hence lost valuable time. Also a number of candidates made assumptions about commutativity which were not justified. Overall, the level and succinctness of meaningful algebraic manipulation shown by candidates was disappointing.
This question was started by the majority of candidates, but only successfully completed by a few. Many candidates seemed to be aware of this style of question, but were either unable to make significant progress or manipulated the algebra in a contorted manner and hence lost valuable time. Also a number of candidates made assumptions about commutativity which were not justified. In part (c) the idea of a proof by contradiction was used by stronger candidates, but weaker candidates were often at a loss as how to start. Overall, the level and succinctness of meaningful algebraic manipulation shown by candidates was disappointing.