How do I plot a line of a fixed length and slope?

I need to plot a line that has some fixed slope at some point, and the length is given, too. How should I do this? Thanks in advance!

Answer 1

[Walter Roberson]

For a line y = m * x + b, to reach a length of L relative to y = b at x=0, the upper range of x should be L/sqrt(m^2+1)

Answer 2

[Thorsten]

 slope = 120/180*pi; length = 10; dx = 10; dy = -20; 
 line([-length/2*cos(slope) length/2*cos(slope)]+dx, [-length/2*sin(slope) length/2*sin(slope)]+dy)