Question: what is meant by rotation in computer graphics

title: Rotation
text: α = cos − 1 ⁡ ( A 11 + A 22 + A 33 − 1 2 ) ( \ displaystyle \ alpha = \ cos ^ ( - 1 ) \ left ( ( \ frac ( A_ ( 11 ) + A_ ( 22 ) + A_ ( 33 ) - 1 ) ( 2 ) ) \ right ) )