How can I change the angle of a line in MATLAB?

Question

I'm trying to compute two lines, with both having the same value for the first Y(1) , but with different lengths. How can I change the angle of the green line, without changing the first Y(1) value, in order to have the same inclination as the red one?

Code:

xx4=[-4.07, -43.9450];
yy4=[1.25, 0.46];

xxlais=[37.1225 -35.93];
yylais=[1.25 0.46];

line(xx4,yy4,'Color','r')
hold on
line(xxlais,yylais,'Color','g')

Answer 1

First compute the expected slope:

slope=(yy4(2)-yy4(1))/(xx4(2)-xx4(1))

Then compute the new Y(2):

yylais(2)=yylais(1)+slope*(xxlais(2)-xxlais(1))