The matrix computed to the lower left is what I came up with to determine if I understand how coefficients are computed, but I can not seem to reason mathematically to compute the matrix both as a fixed function format for a 2d rotation operation clock wise across a reference origin with a unit circle and four quadrants. How can I use the unit circle sign properties and trigonometric functions, namely sin, and cos to find the corresponding coefficients both in the case where the transformation matrix rotates a point 90 degrees clock wise, an operation I am not sure is called possibly a fixed transformation, vs a matrix transformation that transformation that rotates a point using an arbitrary angle on the unit circle. Please clarify. I have not yet grasped this key concept in spite learning how to perform matrix computations in school.
