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  Slope of a perpendicular line  (Read 309 times)
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Offline saucymeatman
« Posted 2013-12-10 21:25:47 »

Hello!

I need to calculate the slope of a perpendicular line, which I can do on a piece of paper :
LineA's slope = 1/3
PerpendicularToLineA's slope = -3/1
(-Run/Rise)

But how do I do this programatically?
lineA.slope = 2;
perpLineA.slope = Huh; (It would equal -1/2 in this case)

I cant find an actual formula anywhere and my line/linesegment classes do not contain rise's/run's only a numerical slope.

Any help is greatly appreciated!
Offline phu004

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« Reply #1 - Posted 2013-12-10 22:08:00 »

If LineA's slope is x1/y1, and the slope for the line that is perpendicular to A is x2/y2,

Then it must satisfy the following:

x1 * x2 + y1 * y2 = 0    //the dot product of 2 vectors (in any dimensions) that are perpendicular to each other is always zero

=>

x1 * x2 = -y1*y2              

=>

x2/y2 = -y1/x1        

Thus if the slop for line A is  2 (i.e x1/y1 = 2),  the slop for the perpendicular line will be -1/2


 
Offline kramin42
« Reply #2 - Posted 2013-12-11 02:46:31 »

perpLineA.slope =  -1/lineA.slope

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Offline Roquen
« Reply #3 - Posted 2013-12-11 06:25:49 »

Don't use slope...use direction.
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