calculate line

[shikur]

Hi

I have a line with coordinated (x1 y1) (x2 y2).
How can I make this line 2 times longer?

Thanks,
shikur

[Fantik]

assuming you want the line to grow from the second coordinates and start at the same spot,

you need to find the current length of the line using the endpoints, and the slope of the line using the endpoints.

then using the same slope, and the new length, find where the new 2nd coordinates need to be, and you are done.