draw a line with known slope and one set of coordinates

I know the coordinates of the starting position of the line (x1,y1). I also know the angle the line makes how to find the second set of coordinates and plot the line?

Answer 1

[dpb]

m=tan(theta);                   % tan()=y/x --> slope
b=y1-m*x1;                      % intercept to pass thru x1,y1 at given slope.
coeff=[m b];                    % coefficient array for convenience
yh=polyval(coeff,[x1 xEnd]);    % evaluate line from x1 to some end point of choice