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A point P has coordinates (x, y) with respect to the original system and coordinates (x′, y′) with respect to the new system. [1] In the new coordinate system, the point P will appear to have been rotated in the opposite direction, that is, clockwise through the angle . A rotation of axes in more than two dimensions is defined similarly.
A rotation in the plane can be formed by composing a pair of reflections. First reflect a point P to its image P′ on the other side of line L 1. Then reflect P′ to its image P′′ on the other side of line L 2. If lines L 1 and L 2 make an angle θ with one another, then points P and P′′ will make an angle 2θ around point O, the ...
For example, in 2-space n = 2, a rotation by angle θ has eigenvalues λ = e iθ and λ = e −iθ, so there is no axis of rotation except when θ = 0, the case of the null rotation. In 3-space n = 3 , the axis of a non-null proper rotation is always a unique line, and a rotation around this axis by angle θ has eigenvalues λ = 1, e iθ , e ...
Call the images of p 2 and p 3 under this reflection p 2 ′ and p 3 ′. If q 2 is distinct from p 2 ′, bisect the angle at q 1 with a new mirror. With p 1 and p 2 now in place, p 3 is at p 3 ″; and if it is not in place, a final mirror through q 1 and q 2 will flip it to q 3. Thus at most three reflections suffice to reproduce any plane ...
The rotation has two angles of rotation, one for each plane of rotation, through which points in the planes rotate. If these are ω 1 and ω 2 then all points not in the planes rotate through an angle between ω 1 and ω 2. Rotations in four dimensions about a fixed point have six degrees of freedom.
All of the cyclic groups are abelian or commutative, but only two of the dihedral groups are: D 1 ~ Z 2 and D 2 ~ Z 2 ×Z 2. In fact, D 3 is the smallest nonabelian group. For even n , the Hermann–Mauguin symbol n m is an abbreviation for the full symbol n mm, as explained below.
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The two rotation planes span four-dimensional space, so every point in the space can be specified by two points, one on each of the planes. A double rotation has two angles of rotation, one for each plane of rotation. The rotation is specified by giving the two planes and two non-zero angles, α and β (if either angle is zero the rotation is ...