Let T 1 </msub> be a reflection of <mi mathvariant="double-struck">R 3

Petrovcic2x

Petrovcic2x

Answered question

2022-06-24

Let T 1 be a reflection of R 3 in the xy plane, T 2 is a reflection of R 3 in the xz plane. What is the standard matrix of transformation T 2 T 1 ?
Here's my thinking so far:
Since the standard matrix for reflections in xy is
[ 1 0 0 0 1 0 0 0 0 ]
Similarly, standard matrix for orthogonal projection in the xz plane is
[ 1 0 0 0 0 0 0 0 1 ]
I could multiply
[ 1 0 0 0 0 0 0 0 1 ] [ 1 0 0 0 1 0 0 0 0 ]
to yield
[ 1 0 0 0 0 0 0 0 0 ]
Could someone confirm for me if this is a valid approach?

Answer & Explanation

Braylon Perez

Braylon Perez

Beginner2022-06-25Added 34 answers

Reflection in the xy plane has matrix
[ 1 0 0 0 1 0 0 0 1 ]
and similar for reflection in the xz plane.
Your matrices, as you say once, are for projection, rather than reflection. If you reflect in the xy plane, the x and y values stay the same, but the z-value becomes its negative.
Your idea of multplying the matrices is correct.

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