# Getting the third point from two points on one line

My question is the following

How can I get point $(x3, y3)$ from points $(x1, y1)$ and $(x2, y2)$ ?

The distance of point $(x3, y3)$ from $(x1, y1)$ is $300$.

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## migrated from stackoverflow.comFeb 18 '11 at 18:23

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Assume

dx = x2 - x1
dy = y2 - y1


Then,

x3 = x1 + dx*k
y3 = y1 + dy*k


The square of distance between p1 and p3 is

(dx^2 + dy^2)*k^2 = 300^2


Now you can find k and then x3 and y3

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It gives me wrong answer –  Sami May 26 '14 at 12:50
@Sami Can you give an example? –  Nikita Rybak Jun 9 '14 at 3:27
Sorry its right. It was only my programming language problem. It tired it in javascript. I later came to know that there i had to use Math.pow(x,2) instead of x^2 –  Sami Jun 9 '14 at 8:43