octave

x=[-2;0;1]; y=[-5; 0; 1];b=y;
A=[x [1;1;1]]
alfa=-6:0.5:6;beta=alfa;
[AL,BE]=meshgrid (alfa,beta);
Z=0.5*(-AL+3*BE);
mesh(AL,BE,Z)
hold on
plot3([-5],[0],[1],'x')
projb=A*inv(A'*A)*A'*b;
plot3([projb(1,1)],[projb(2,1)],[projb(3,1)],'o')
axis ([-6, 6,-6 , 6, -6,6], "square")
legend('CS(A)','b','projeccao de b' );