Conic Sections - Examples & Applications

This section provides step-by-step examples on how to work with the equations of conic sections. You will learn to identify the type of conic from a general equation, convert equations into standard form by completing the square, and extract key geometric properties like the center, vertices, and foci.

The General Equation

The general equation Ax2+Bxy+Cy2+Dx+Ey+F=0Ax^2 + Bxy + Cy^2 + Dx + Ey + F = 0 can be converted to standard form by completing the square.

Example

Problem: Convert x2+y2−6x+4y−12=0x^2 + y^2 - 6x + 4y - 12 = 0 into standard form.

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Identifying Conic Sections

The general equation for a conic section is Ax2+Bxy+Cy2+Dx+Ey+F=0Ax^2 + Bxy + Cy^2 + Dx + Ey + F = 0. Assuming the axes are not rotated (B=0B = 0), you can quickly identify the shape by looking at the coefficients AA and CC.

Example

Problem: Identify the type of conic section represented by each of the following equations:

  1. 4x2+4y2−16x+8y−5=04x^2 + 4y^2 - 16x + 8y - 5 = 0
  2. 9x2−y2+18x+4y+5=09x^2 - y^2 + 18x + 4y + 5 = 0
  3. y2−4x−6y+17=0y^2 - 4x - 6y + 17 = 0
  4. 2x2+5y2−8x−30y+13=02x^2 + 5y^2 - 8x - 30y + 13 = 0

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Circles

The standard form for a circle is (x−h)2+(y−k)2=r2(x - h)^2 + (y - k)^2 = r^2, where (h,k)(h, k) is the center and rr is the radius.

Example

Problem: Find the center and radius of the circle given by the equation x2+y2+6x−4y−12=0x^2 + y^2 + 6x - 4y - 12 = 0.

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Parabolas

The standard form for a vertical parabola is (x−h)2=4p(y−k)(x - h)^2 = 4p(y - k). For a horizontal parabola, it is (y−k)2=4p(x−h)(y - k)^2 = 4p(x - h).

Example

Problem: Find the vertex, focus, and directrix of the parabola given by y2+8x−2y−15=0y^2 + 8x - 2y - 15 = 0.

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Ellipses

The standard form of an ellipse is (x−h)2a2+(y−k)2b2=1\frac{(x-h)^2}{a^2} + \frac{(y-k)^2}{b^2} = 1. The larger denominator determines the major axis.

Example

Problem: Find the center, vertices, and co-vertices of the ellipse: (x+2)29+(y−4)225=1\frac{(x+2)^2}{9} + \frac{(y-4)^2}{25} = 1.

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Standard Forms and Properties of Conics

Each type of conic section has unique properties—foci, directrices, asymptotes—that can be derived from its standard form equation.

Example

Problem: For the ellipse (x−1)216+(y+2)29=1\frac{(x - 1)^2}{16} + \frac{(y + 2)^2}{9} = 1, find the center, vertices, and foci.

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