Finding an Angle between a Line and a Line SegmentDate: 10/29/95 at 13:12:50 From: Anonymous Subject: Geometry or Trig, Find angle What is the best way to find the angle between a line and a line segment that both originate at the same point? Date: 11/1/95 at 12:4:16 From: Doctor Andrew Subject: Re: Geometry or Trig, Find angle If you know the slope of each line you can use inverse tangent to find the angle of each line and then find their difference. Another way is to use dot products. Suppose you have two vectors from the origin: (a,b) and (a',b') (a,b) dot (a',b') = |(a,b)| |(a',b')| cos angle. So, the angle is the inverse cos of (a,b) dot (a',b') / (|(a,b)| |(a',b')|) Remember that (a,b) dot (a',b') = aa' + bb' and |(a,b)| = sqrt(a^2 + b^2). -Doctor Andrew, The Geometry Forum |
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