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February 28th, 2018, 05:23 AM  #1 
Newbie Joined: Feb 2018 From: Brazil Posts: 1 Thanks: 0  Calculate third point from 2 points and an angle
I'm having a hard time putting together a formula. I have 2 points (x0, y0) and (x1, y1) and an angle (k). Using this information I need to calculate a third point that is k degrees from the previous 2 points. The problem is something like this: https://servimg.com/view/19866823/2 Is it possible to do that? Thank you for your attention. Last edited by skipjack; February 28th, 2018 at 07:20 AM. 
February 28th, 2018, 07:41 AM  #2 
Global Moderator Joined: Dec 2006 Posts: 19,722 Thanks: 1807 
Do you require the two lines shown in the diagram to be the same length? If so, call that length r. The point C will then be (r*cos(θ), r*sin(θ)), where r = √((x1  x0)² + (y1  y0)²) and the angle θ is chosen appropriately. Do you see how to choose θ? Note that this is essentially a trigonometry question, so I've moved the thread to the trigonometry forum. If the point C is obtained by a rotation, as suggested above, its coordinates are given by a standard formula that is mathematically equivalent to what I referred to above, but has a more elegant form, especially if described by use of a rotation matrix. 

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angle, calculate, point, points 
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