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nns91
Mar2-09, 08:58 PM
1. The problem statement, all variables and given/known data

Suppose n is normal to a plane and v is parallel to the plane. Describe how you would find a vector u that is both perpendicular to v and parallel to the plane.



2. Relevant equations

Cross product, dot product

3. The attempt at a solution

Since u is perpendicular to v, u dot v = 0. U is also parallel to the plane so u will be perpendicular to n, so u dot n=0.

How would I do the rest of it ?

csprof2000
Mar2-09, 10:10 PM
Well, I can't give you the solution, but I will tell you that if I gave you a hint, you'd probably know it. Let's try.

You've used the dot product. Does the cross product help?

Dick
Mar2-09, 10:11 PM
You didn't use the cross product. axb is perpendicular to both a and b, right?

nns91
Mar2-09, 10:18 PM
Oh so u is basically n cross v ?

Dick
Mar2-09, 10:22 PM
Oh so u is basically n cross v ?

Sure. Or any multiple thereof.