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April 23rd, 2014, 10:16 AM  #1 
Newbie Joined: Apr 2014 From: Netherlands Posts: 2 Thanks: 0  Calculating intersecting lines in 3D
Hello, I am trying to calculate if two lines intersect in 3D, and where the intersecting point is. Now I found this on the internet, but I do not understand everything they explain. linear algebra  Find intersection of two 3D lines  Mathematics Stack Exchange In the answer of robjohn with the colored text, I understand that X stands for Crossproduct. But I do not understand the constant part and how he comes up with the number 400. (As far as I know a constant is a variable that does not change, I do not understand how he gets this 400 out of a vector in this situation) Also I do not understand how t becomes 1/4 in this part: 600−800t=400 t=1/4 Is there anyone who can explain me how this works? Thanks in advance Alexander 
April 24th, 2014, 01:21 AM  #2 
Newbie Joined: Apr 2014 From: Netherlands Posts: 2 Thanks: 0 
I do understand how t=1/4, it was late yesterday when I posted this. but I still do not get where the 400 comes from.

May 4th, 2014, 12:37 PM  #3  
Newbie Joined: May 2014 From: India Posts: 7 Thanks: 0 
Every point on the line can be written as $\displaystyle (5,5,4)t.[(5,5,4)(10,10,6)]$ So when you multiply $\displaystyle (20,20,0)$ which is perpendicular to $\displaystyle (5,5,2)$ it is always is equal to constant since t term cancels out....Now assuming you got the 'constant' concept. Quote:
 

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