1. The problem statement, all variables and given/known data Here are two displacements, each measured in meters: A. 4i+5j-6k B. -1i+2j+3k What is the component of A that is perpendicular to the direction of B and in the plane of A and B.? 2. Relevant equations The book gave me a hint to use this equation: http://puu.sh/fFya9/3d102e2d2f.png [Broken] c being the magnitude of the result of A cross B. a and b being the magnitudes of vectors A and B. 3. The attempt at a solution I plugged the values into that: c=(8.775)*(3.742)*sin(111.438) c=30.564 I don't see how that is supposed to help me. A cross B gives me the vector: C=27i-6j+13k This vector is perpendicular to the A,B plane. Would I need to cross C by B again to get it back in the A,B plane? After doing that would I need to use this equation to find the final component part? Doing that gives me: D=-44i-94j+48k A dot D=-934 -934=8.775*114.35*cos(phi) phi=158.56 I think this is the angle between vectors A and D. Then is it just a*cos(158.56) 8.77*cos(158.56)=-8.17 I'm not 100% sure that is correct as I feel I messed up with being able to cross product twice to get back on the A,B plane. Your help is greatly appreciated.