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Ch. 7 - Conic Sections
Blitzer - College Algebra 8th Edition
Blitzer8th EditionCollege AlgebraISBN: 9780136970514Non è quello che usi tu?Cambia libro di testo
Capitolo 8, Problema 87

Find the standard form of the equation of an ellipse with vertices at (0, -6) and (0, 6), passing through (2, 4).

Guida verificata passo dopo passo
1
Identify the center of the ellipse by finding the midpoint of the vertices. Since the vertices are at (0, -6) and (0, 6), the center is at (0, 0).
Determine the orientation of the ellipse. The vertices lie on the y-axis, so the major axis is vertical. This means the standard form of the ellipse equation is \( \frac{x^2}{b^2} + \frac{y^2}{a^2} = 1 \), where \(a\) is the distance from the center to a vertex along the y-axis.
Calculate \(a\), the distance from the center to a vertex. Since the vertices are at (0, ±6), \(a = 6\). So, \(a^2 = 36\).
Use the point (2, 4) that lies on the ellipse to find \(b^2\). Substitute \(x = 2\), \(y = 4\), and \(a^2 = 36\) into the ellipse equation: \( \frac{2^2}{b^2} + \frac{4^2}{36} = 1 \).
Solve the equation from step 4 for \(b^2\) by isolating \( \frac{4}{b^2} \), then multiply both sides by \(b^2\) and solve for \(b^2\). This will give you the value needed to write the standard form of the ellipse.

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Standard Form of an Ellipse

The standard form of an ellipse equation depends on the orientation of its major axis. For a vertical major axis centered at the origin, the equation is (x^2 / b^2) + (y^2 / a^2) = 1, where 'a' is the distance from the center to a vertex along the y-axis, and 'b' is the distance along the x-axis. Understanding this form helps in identifying the ellipse's shape and size.
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Graph Ellipses at Origin

Vertices of an Ellipse

Vertices are the points on the ellipse farthest from the center along the major axis. Given vertices at (0, -6) and (0, 6), the center is at the origin (0,0), and the length of the major axis is 12, so a = 6. Knowing the vertices allows determination of 'a' in the ellipse equation.
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Foci and Vertices of an Ellipse

Using a Point to Find the Ellipse Parameters

Substituting a known point on the ellipse into the standard form equation allows solving for the unknown parameter 'b'. Here, the point (2, 4) lies on the ellipse, so plugging in x=2 and y=4 helps find 'b', completing the equation. This step is essential to fully define the ellipse.
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