# Dot and cross product problem

dot product and cross product. i (think dot product is like eg (1,2,4).(2,4,5) = 30 and cross product is like eg(1,2,4)x(2,4,5)=2, 8, 20) but im not sure... and is there an order like in a.bxc do u do bxc and then.a or do u go normal left to right. but if left to right whats the rule in when u multiply one number by a coordinante or vector...
please help

## Answers and Replies

and is there an order like in a.bxc do u do bxc and then.a or do u go normal left to right.

A dot product operation on two vectors results in a scalar i.e. a number [not a vector]. Whereas, the cross product always results in a vector. As for a.(b x c), you CANNOT open the bracket as: (a.b x a.c). This is because cross product is operation that is done on vectors and not on scalars, whereas both, a.b and a.c are scalars.

So, you have to first find out the cross product of b & c, and then solve for the dot product of the resultant vector and a to get your answer.

thanks for clearing that up 