Troubleshooting - A Guide to MATLAB for Beginners and Experienced Users - page 258

The matrix A2 is singular. In fact
det(A2)
ans =
0
(c)
A3=[13-24;-234-1;-4-312;23-41];b3=[1;1;
1; 1];
x = A3\b3
x=
-0.5714
0.3333
-0.2857
-0.0000
A3*x
ans =
1.0000
1.0000
1.0000
1.0000
(d)
symsabcdxyuv;
A4 = [a b; c d]; A4\[u; v]
ans =
[ -(b*v-u*d)/(a*d-c*b)]
[ (a*v-c*u)/(a*d-c*b)]
det(A4)
ans =
a*d-c*b
Thedeterminantofthecoefficientmatrixisthedenominatorintheanswer.
So the answer is valid only if the coefficient matrix is non singular.