# How to translate a point on a line by a distance "e" ?

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bh dhouha on 5 May 2015
Commented: bh dhouha on 5 May 2015
I have the line given by the points A and B . The line is in the form [a b c] where the equation is ax+by+c=0. I would like to know the coordinates of the points C and D (figure) which are on the same line but distant of "e" from the point B. I found some functions like "translation" etc but they work with matrices and are too complicated. I just would like to give the parameters of the line (a b c), the points A and B, distance e and get the coordinates of C and D as result. Thanks James Tursa on 5 May 2015
de = e * (A - B) / norm(A - B);
D = B + de:
C = B - de;
bh dhouha on 5 May 2015
thanks a lot

Image Analyst on 5 May 2015
This is just simple high school trig/algebra. You know the slope of the line, -a/b, so you know the angle, and so you can find the new x and y values of C and D with sin and cos and the value of e.
bh dhouha on 5 May 2015
I know but i'm working on complicated things so sometimes i forget about details like this. Thanks anyway.