# It's a bird! It's a plane! It's not superman...

**Geometry**Level 2

A system of three linear equations with three variables \( x, y, z \) in the form

\[ \left\{\begin{matrix} ax+by+cz = d\\ ex+fy+gz = h \\ ix+jy+kz = l \end{matrix}\right.\]

with \((a, b, c, d, e, f, g, h, i, j, k, l) \in \mathbb{Z} \) could be considered geometrically as three different planes intersecting each other in various ways, depending what those coefficients are. Some of the coefficients may be equal to other coefficients--or not.

Let \( \text{A} \) be the coefficient matrix of that above system. If \( \text{det(A)} = 0 \), which of the following could be true about the system?

**A.** The planes are all parallel to each other.

**B.** A line is formed by the intersection of all three planes.

**C.** The planes form a triangular prism missing the triangular faces.

**D.** The planes all intersect at a single point.