question below: (about vectors)

Question

anonymous · Answer

attachment

wolfe8 · Answer

I think you just do some substitutions

anonymous · Answer

i tried doing that but i got stuck because of the dot product..

wolfe8 · Answer

Show me what you did?

anonymous · Answer

try to imagine it graphicly:
|dw:1386711536286:dw|
like you should know, dot product of two vectors give a real number. This number is the length of the projection of one of the vectors onto anothers direction. So c=(b . a)a means that c and a are bouth in same direction. Or to say it other way c is (b.a) times a. This is give you some insigth on how you should continue for the proof

anonymous · Answer

sry a is missing in the previous picture. Here it goes:
|dw:1386711968538:dw|

anonymous · Answer

oh okay, i got what you mean:
|dw:1386711903054:dw|