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
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.