MATLAB: How to measure angle between the lines

Question

I have plotted the lines with the following code.

x = [3 0];

y = [0 9];

line(x,y);

a = [1 2];

b = [0 3];

line(a,b);

axis([0 4 0 10]);

Now, how can I measure the angle between these lines?

Answer 1

 diff = (atan((y(2)-y(1))/(x(2)-x(1))) - atan((b(2)-b(1))/(a(2)-a(1)))) * 180/pi;