Which property is preserved under all affine transformations T(v⃗)=Mv⃗+b⃗T(\vec{v}) = M\vec{v} + \vec{b}T(v)=Mv+b with det(M)≠0\det(M) \neq 0det(M)=0?
Distance between points
Parallelism of lines
Angles between lines
Area of regions