Matrix multiplication confussion or error?

I got very confused by the question 7 of the Vector and Matrix Operations, Types of Matrices questionary. In the lesson of “Matrix multiplication” we’ve been told to invert the order of the matrices to do the dot product: M2 · M1, but in the questionary the correct answer comes from multiplying M1 · M2. Is the questionary wrong? If not, could anyone explain me why are we using to different methods to dot multiplying the matrices? Thank you!

Hi @David73!

Welcome to our community!

The inversion that happens in the video is just due to the geometric interpretation of a composition of linear transformations. If we have T_1 and T_2 linear transformations with M_1 and M_2 corresponding matrices, then the matrix related to composition as T_1 \circ T_2 is given by M_2 \cdot M_1. However, performing a matrix calculation in general, we do not make such inversion.


Thank you very much!!!