Which of the following expressions are meaningful? which are meaningless? explain. (a) (a · b) · c (a · b) · c has because it is the dot product of . (b) (a · b)c (a · b)c has because it is a scalar multiple of . (c) |a|(b · c) |a|(b · c) has because it is the product of . (d) a · (b + c) a · (b + c) has because it is the dot product of . (e) a · b + c a · b + c has because it is the sum of . (f) |a| · (b + c) |a| · (b + c) has because it is the dot product of .