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Abel's theorem in problems and solutions - School of Mathematics

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112 Problems <strong>of</strong> Chapter 1<br />

45. H<strong>in</strong>t. Use the result <strong>of</strong> Problem 41. The isomorphism is<br />

46. H<strong>in</strong>t. Use the result <strong>of</strong> Problem 27. The isomorphism is<br />

47. Let Thus<br />

Multiply<strong>in</strong>g the two<br />

members <strong>of</strong> this equality by <strong>in</strong> the group F one obta<strong>in</strong>s<br />

<strong>and</strong><br />

48.<br />

(see 47)<br />

It follows that<br />

49. Let be a non-zero <strong>in</strong>teger. Thus<br />

Let <strong>and</strong> be the orders<br />

<strong>of</strong> the elements <strong>and</strong> Thus <strong>and</strong> (see 47)<br />

Therefore On the other h<strong>and</strong>, so<br />

Hence<br />

50. Answer. a) The sole group is b) The sole group is Solution.<br />

a) Let <strong>and</strong> be the elements <strong>of</strong> the group <strong>and</strong> the unit element. Thus<br />

<strong>and</strong> only the product rema<strong>in</strong>s unknown.<br />

If then (see 24) one obta<strong>in</strong>s the contradiction<br />

It follows that <strong>and</strong> that there exists only one group, conta<strong>in</strong><strong>in</strong>g 2<br />

elements. It is the cyclic group<br />

b) Let be the elements <strong>of</strong> the group <strong>and</strong> the unit element. We<br />

need to know to which elements the products correspond.<br />

If one obta<strong>in</strong>s the contradiction if one obta<strong>in</strong>s the<br />

contradiction It follows that Consequently If<br />

one has the contradiction If one has the<br />

contradiction It follows that Thus <strong>and</strong> there exists<br />

only one group conta<strong>in</strong><strong>in</strong>g 3 elements. S<strong>in</strong>ce this<br />

group with elements is the cyclic group<br />

51. Answer. For example, the group <strong>of</strong> rotations <strong>of</strong> the square is not<br />

isomorphic to the group <strong>of</strong> symmetries <strong>of</strong> the rhombus, because <strong>in</strong> the<br />

former there is an element <strong>of</strong> order 4, whereas <strong>in</strong> the latter there is not<br />

(see 49).<br />

52. Consider the map If takes all the real values, takes<br />

exactly once all the real positive values. Hence is a bijective mapp<strong>in</strong>g

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