Consider following system of equations:
$\begin{bmatrix} 1 &2 &3 &4 \\ 5&6 &7 &8 \\ a&9 &b &10 \\ 6&8 &10 & 13 \end{bmatrix}$$\begin{bmatrix} x1\\ x2\\ x3\\ x4 \end{bmatrix}$=$\begin{bmatrix} 0\\ 0\\ 0\\ 0 \end{bmatrix}$
The locus of all $(a,b)\in\mathbb{R}^{2}$ such that this system has at least two distinct solution for ($x_{1},x_{2},x_{3},x_{4}$) is
- a parabola
- a straight line
- entire $\mathbb{R}^{2}$
- a point