Eric Arnebäck on Twitter: "Below, I have written down a concise and sweet derivation of the 2D rotation matrix, for future reference. Following this, the 3D rotation matrices can easily be derived,
Rotate a matrix by 90 degree without using any extra space | Set 2 - GeeksforGeeks
Matrix Rotations
Rotation matrix - Wikipedia
Derivation: Rotation matrix in counterclockwise direction | Sumant's 1 page of Math
Rotating matrices - The DO Loop
matrices - Which direction is clockwise when rotating around x-axis in 3D? - Mathematics Stack Exchange
Clockwise Rotation Matrix by amit kumar - Issuu
Matrix rotation by 90 degrees clockwise and anticlockwise