how to extend line of image

hello everyone,

i have detect two coordinate of pixel which is (1,1) and (2,5). i already join the two coordinate to make a line. i have done it.. my question is i want to extend the line to the end. how to do this.. here i attach picture illustration for your understanding. help me please how to extend line

http://i1259.photobucket.com/albums/ii548/msaiful89/line.png

Answer 1

[Walter Roberson]

Standard algebra. Solve the equation of a line, y = m*x + b, knowing that m = (y2-y1)/(x2-x1) . Use your initial data to calculate m and b, then use those two to fill in the line.

Answer 2

[Stephen]

if... x1=1,x2=2 and... y1=1,y2=5

(2,5)-(1,1)=m=(1,4), is your slope

so m1=1,m2=4

try

plot([x1 x2]+1e6*[-m1 m1],[y1 y2]+1e6*[-m2 m2])

brute force wins again