Answer: (x-h)2 + (y-k)2 = r2.
- A (x-h)2 + (y-k)2 = r2
- B (x-h)2 - (y-k)2 = r2
- C x2 + y2 = r
- D (x+h)2 + (y+k)2 = r
Correct answer: A. (x-h)2 + (y-k)2 = r2
Explanation: The standard circle equation centered at (h,k) with radius r is (x-h)2 + (y-k)2 = r2.
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.