Conic Section
Chapter Summary
A Conic Section is the locus of a point moving in a plane such that the ratio of its distance from a fixed point (focus) to its fixed line (directrix) is a constant known as the eccentricity ($e$). Depending on the value of $e$, conics are classified into four fundamental curves: Circle ($e=0$), Parabola ($e=1$), Ellipse ($0 < e < 1$), and Hyperbola ($e > 1$). Mastery of the general second-degree equation $Ax^2 + Bxy + Cy^2 + Dx + Ey + F = 0$ and its discriminant $B^2 - 4AC$ is crucial for identifying these curves in board exams.
The Parabola is defined by a set of points equidistant from the focus and directrix. You must memorize the standard equations for both horizontal and vertical orientations (e.g., $y^2 = 4ax$ and $x^2 = 4ay$), along with their key geometric properties: vertex, focus, directrix, axis of symmetry, and length of the latus rectum ($4a$). Examiners frequently test your ability to find these elements when given a scrambled equation by completing the square.
For the Ellipse and Hyperbola, focus heavily on their standard center-form equations $\frac{x^2}{a^2} + \frac{y^2}{b^2} = 1$ and $\frac{x^2}{a^2} - \frac{y^2}{b^2} = 1$ (and their vertical counterparts). You need to be fluent in calculating the vertices, foci, eccentricity ($c/a$), major/minor axes (for ellipses), transverse/conjugate axes (for hyperbolas), and asymptotes (for hyperbolas). Special attention should be given to shifted conics where the center is at $(h, k)$ rather than the origin.
Expect questions requiring you to write the equation of a conic given specific geometric conditions (like foci and ends of the major axis) or tangent-related problems. In the Punjab, Federal, and other BISE board exams, long-answer (subjective) questions heavily feature sketching or deriving properties of conics and reducing general equations to standard forms. Practice sketching graphs clearly, as examiners award marks for properly labeled axes, foci, and vertices.
Important Questions
- Find the equation of the parabola with focus at (2, 0) and directrix x = -2.4 marks
- Find the vertices, foci, and eccentricity of the ellipse 9x^2 + 16y^2 = 144.5 marks
- Find the equations of the tangents to the circle x^2 + y^2 = 25 parallel to the line 3x - 4y + 7 = 0.5 marks
- Find the center and radius of the circle represented by the equation x^2 + y^2 - 6x + 8y - 24 = 0.3 marks
- Find the equation of the hyperbola whose foci are (±5, 0) and the transverse axis is of length 8.5 marks
- Find the length of the major and minor axes of the ellipse 4x^2 + 9y^2 = 36.3 marks
- Show that the lines x - 2y = 3 and 2x + y = 5 are tangents to the circle x^2 + y^2 = 5.5 marks