The general quadratic (conic) equation is:
Ax² + Bxy + Cy² + Dx + Ey + F = 0
Discriminant Test
Δ = B² − 4AC
- Δ < 0 → Ellipse (circle if A = C and B = 0)
- Δ = 0 → Parabola
- Δ > 0 → Hyperbola
Ellipse & Circle
Ellipse: (x−h)²/a² + (y−k)²/b² = 1
Circle: (x−h)² + (y−k)² = r²
- h, k: Center of the ellipse/circle.
-
a, b: Semi-axes lengths (a = semi-major, b =
semi-minor). For a circle a = b = r.
- r: Radius (special case when a = b).
-
Foci (ellipse): Along the longer axis at
distance c where c² = a² − b².
-
Major axis: The longer diameter (length 2a).
Minor axis length 2b.
Parabola
Vertical: (x−h)² = 4p(y−k)
Horizontal: (y−k)² = 4p(x−h)
- h, k: Vertex (turning point).
-
p: Focal distance: |p| is distance from vertex
to focus and to directrix.
-
Focus: (h, k + p) for vertical; (h + p, k) for
horizontal.
-
Directrix: y = k − p (vertical case); x = h − p
(horizontal case).
-
Axis of symmetry: Line through vertex & focus
(x = h or y = k).
Hyperbola
Horizontal: (x−h)²/a² − (y−k)²/b² = 1
Vertical: (y−k)²/a² − (x−h)²/b² = 1
- h, k: Center.
-
a: Distance from center to each vertex on the
transverse axis.
-
b: Conjugate semi-axis; shapes the asymptote
slopes.
-
c: Focal distance with c² = a² + b²; foci lie
along the transverse axis at (h ± c, k) or (h, k ± c).
-
Vertices: (h ± a, k) or (h, k ± a) depending on
orientation.
-
Asymptotes: y − k = ±(b/a)(x − h) (horizontal)
or y − k = ±(a/b)(x − h) (vertical).
If B ≠ 0, rotate axes to remove the xy term before fitting one of
these forms.