# Calculating normal vector

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If I have, let's say, a rectangle, how can I calculate a vector perpendicular to it? Assume the coordinates of the corners are: -1,-1,0 1,-1,0 1,1,0 -1,1,0 So I have a square that runs parallel with the x- and y-axis. The normal vector would be 0,0,1 (or 0,0,-1 depending on what side you consider up). If I have the coordinates of the corners, how can I calculate the normal vector?

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You use the cross product of 2 vectors to find the normal.

Create two vectors from your rectangle using two of the edges.

http://mathworld.wolfram.com/CrossProduct.html

That will explain cross products to you.

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