Answer: absent (zero).
- A absent (zero)
- B clearly present
- C strongly negative
- D extremely large
Correct answer: A. absent (zero)
Explanation: A circle needs equal x² and y² coefficients and no xy (cross) term.
All four conics form a single family distinguished only by eccentricity: a circle is the most "closed" (e=0), an ellipse is an elongated closed curve, a parabola is the borderline open curve (e=1), and a hyperbola has two separate open branches (e>1).
Concept context
Study circles, parabolas, ellipses, and hyperbolas as curves formed by intersecting a plane with a double cone, with their standard equations and key properties.