MATLAB: Vectors must be the same length.

Question

Recently started learning MatLab, trying to plot a function graph.

{2a+b=1
 2a-b=7

I run this code, I get "Vectors must be the same length."

Error in Untitled2 (line 9)

plot(X,Y1,X,Y2);

Code:

A=[2,1;2,-1]
B=[1;7]
d=det(A)
X=inv(A)*B
A*X
X=-2:0.5:2;
Y1=(-2*A+1)/1;
Y2=(-2*A+7)/(-1);
plot(X,Y1,X,Y2);
grid on

Answer 1

You overwrite X:

A=[2,1;2,-1]
B=[1;7]
d=det(A)
X=inv(A)*B
A*X
%X=-2:0.5:2;
Y1=(-2*A+1)/1;
Y2=(-2*A+7)/(-1);
plot(X,Y1,X,Y2);
grid on

To avoid this i commented the overwriting line out, because it is not used in the following code.