Extend a line segment a specific distance

Question

I am trying to find a way to extend a line segment by a specific distance. For example if I have a line segment starting at 10,10 extending to 20,13 and I want to extend th

Answer 1

If you already have the slope you can compute the new point:

x = old_x + length * cos(alpha);
y = old_y + length * sin(alpha);

I haven't done this in a while so take it with a grain of salt.