What do you think might be true about:

a · b · c

It makes no sense. Remember that the dot product of two vectors (or column matrices) makes a real number. There is no such thing as the dot product between a real number and a vector (or column matrix).

There is no such thing as the dot product between a real number and a column matrix.

a · b · c= real· c<=== garbage

or:

a · b · c=a ·real <=== garbage

When dealing with dot products, keep track of the types of operands and results, as illustrated by the previous question.