A = rand(3, 4);

for i=1:4
    M = A;
    M(:,i) = [];
    X(i,1) = - det(M) * (-1)**i;
end
X = X / X(1);

M = A(:,2:$);
B = -A(:,1);

X2 = [1; M \ B];

disp(norm(X - X2))