Perpendicular Vector Resolute

PLEASE HELP

http://i47.tinypic.com/2jb8unp.jpg

Me and my friends keep getting 1/9(13i - 20j - 23k) for this question and can't work out why the sign is incorrect, I am investigating whether or not it is a typo but am wondering what you guys think the answer is?

Also sorry if this is the wrong board, I wasn't sure if it was algebra or geometry...

Re: Perpendicular Vector Resolute

Re: Perpendicular Vector Resolute

Re: Perpendicular Vector Resolute

Let the first vector be a and the second one b. Make a unit vector in the direction of b. Work out the scalar product of this unit vector with a. This then is the magnitude of the resolute in the direction of b so you can work out the vector for this resolute. Then do the vector subtraction of this from a to get the required vector.