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Quick Question on Vectors in FP3 (for exam tomorrow)

If I wanted to find the acute angle between 2 lines, I'd use the dot product with cosx.

* But if I wanted to find the acute angle between an angle of a plane and a line, would I use sinx/cos(90-x) instead of simple cosx? Is that correct?
* And if I wanted to find the acute angle between two planes, which would I use?

I saw this in a paper I just did and I remember my teacher saying something about it, but I can't remember the rule for it. :/

EDIT: Never mind, I think I understand why. If anyone reads this and is also wondering, plane+line is sinx and plane+plane is cosx. And I kind of get why, so hopefully I'll remember tomorrow, haha.

http://www.vitutor.com/geometry/distance/line_plane.html
http://www.vitutor.com/geometry/distance/angle_planes.html
(edited 8 years ago)

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