Matrix in 3 dimension
3-D
Extend 2-D to 3-D, each direction has 3 elements.
Combine these transformed vector by column, we can get transformation matrix.
Rotate 90 degree on y-axis
We can also apply this transformation matrix to a vector that needs to be transformed.
3-D matrix multiplication is like doing a transformation after another in 2-D.
Reference
https://www.3blue1brown.com/topics/linear-algebra