Thread: Perpendicular Vector Resolute

PLEASE HELP



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...

first, the dot product of (1/9)(13i- 20j- 23k) and (2i- j+ 2k) is (1/9)(26+ 20- 46)= 0 so that IS perpendicular to 2i- j+ 2k to begin with!

On the other hand, the dot product of (1/9)(13i+ 20j- 23k) and (2i- j+ 2k) is (1/9)(26- 20- 46) is NOT 0 so they are not perpendicular so D is the answer in the book it is not correct.

[B[/B]

Originally Posted by AndrewP

PLEASE HELP



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...

Your answer is correct. Apologies for my earlier incorrect reply.