I think there are a couple slides missing from in-person lecture?

E.g. the slides about Which normals to use, and corrrectly calculating normals with matrix transformation

waleedlatif1

I have a question about the following slide about incorrectly transforming normal vectors. In the case of shearing, I don't understand why the vector in the middle image is incorrect, because a normal vector has to be perpendicular to the surface, which to me intuitively it seems like is. I see the derivation and why using the inverse transpose of M works mathematically, but geographically I can't get myself to understand why the normal vector that results from M does not work.

I think there are a couple slides missing from in-person lecture?

E.g. the slides about Which normals to use, and corrrectly calculating normals with matrix transformation

I have a question about the following slide about incorrectly transforming normal vectors. In the case of shearing, I don't understand why the vector in the middle image is incorrect, because a normal vector has to be perpendicular to the surface, which to me intuitively it seems like is. I see the derivation and why using the inverse transpose of M works mathematically, but geographically I can't get myself to understand why the normal vector that results from M does not work.