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.
What is 2( -1, 2)T · ( 4, 1 )T ?