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Isometries of R3
I am reading Aigli Papantonopoulou's book Algebra: Pure and applied.
Exercise 18 of Chapter 14:Symmetries reads as follows:
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"Describe all the isometries of
that map the point (1,1,1) to (1,0,0) and express them in the form
as in Theorem 14.21, and in terms of S(
) = A
+ b as in Corollary 14.22
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I would really appreciate help with this problem.
Peter
Details from Papantonopoulou follow:
On pages 462 - 463 we find:
Possible isometries of
or
include:
(1) Translations: These are of the form
=
+ b
(2) Rotations: These are of the form
for some A
SO(n). We write
for a rotation by an angle
(about some axis through the origin)
(3) Reflections: These are given by
for some A
O(n) with det A = -1, that is A not in SO(n). We write r for reflections given by the matrices
O(2)
O(3)
Since SO(n) is a subgroup of O(n) of index 2, every reflection is of the form
r
Theorem 14.21
An isometry S of
or
can be uniquely expressed as
S =
where i = 0 or 1
Corollary 14.22
An isometry S of
or
can be uniquely expressed as
S(
) = A
+ b where A
O(n) and b

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Re: Isometries of R3
the only part of this worth investigating is the translation part, because any element of O(3) preserves the origin. so ask yourself: if x-->x+b takes (1,1,1) to (1,0,0), what must the 3-vector b be?