Question 8 • Precalculus
For a conic Ax² + Bxy + Cy² + Dx + Ey + F = 0, a parabola has B² − 4AC = 0, provided the equation is not degenerate. In A and D, only one variable is squared, so B² − 4AC = 0. In C, B² − 4AC = (−12)² − 4(9)(4) = 0; its squared part is (3x − 2y)², and the linear terms vary along the direction where that squared part is zero, so it is a parabola. B has a negative discriminant, and E has a positive one, so neither is a parabola.
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