Chapter 10: Problem 347
Graph the hyperbola, labeling vertices and foci. $$2 y^{2}-x^{2}-12 y-6=0$$
Short Answer
Expert verified
The hyperbola has vertices at \((0, 3 \pm 2\sqrt{3})\) and foci at \((\pm 6, 3)\).
Step by step solution
01
Rearrange and Complete the Square
Begin with the equation: \[ 2y^{2} - x^{2} - 12y - 6 = 0 \]First, move the constant to the other side:\[ 2y^{2} - 12y - x^{2} = 6 \]Now, complete the square for the \(y\)-terms. Factor out 2:\[ 2(y^{2} - 6y) - x^{2} = 6 \]To complete the square, add and subtract \( (-\frac{6}{2})^2 = 9 \):\[ 2((y - 3)^{2} - 9) - x^{2} = 6 \]Thus, simplifying gives:\[ 2(y - 3)^{2} - 18 - x^{2} = 6 \]
02
Further Simplify
Add 18 to both sides:\[ 2(y - 3)^{2} - x^{2} = 24 \]Divide every term by 24 to get the equation in standard form:\[ \frac{x^{2}}{24} - \frac{(y - 3)^{2}}{12} = 1 \]
03
Identify Hyperbola Details
The standard form of the hyperbola is:\[ \frac{x^{2}}{24} - \frac{(y - 3)^{2}}{12} = 1 \]This is a hyperbola that opens left and right because the \(x\)-term is positive. The center is at \((0, 3)\).
04
Find Vertices
The distance from the center to each vertex along the \(y\) is determined by the value under \((y - 3)\) in the standard form. That value is \(\sqrt{12} = 2\sqrt{3}\).Vertices are at \(y = 3 \pm 2\sqrt{3}\).
05
Find Foci
To find the foci, use the formula \( c^{2} = a^{2} + b^{2} \). Here, \(a = \sqrt{24} = 2\sqrt{6}\) and \(b = \sqrt{12} = 2\sqrt{3}\).Thus, \(c^{2} = (2\sqrt{6})^2 + (2\sqrt{3})^2 = 24 + 12 = 36\).This gives \(c = 6\).So, the foci are located at \((\pm 6, 3)\).
06
Draw and Label the Graph
Plot the center at \((0, 3)\). Plot the vertices at \((\pm 2\sqrt{6}, 3)\). Mark the foci at \((\pm 6, 3)\). Draw smooth curves extending from the vertices, opening along the x-axis.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Completing the Square
When dealing with quadratic equations, completing the square is a useful technique to rewrite the equation in a form that is easier to interpret or solve. Let's break down how it's done using the original hyperbola equation:
\(2y^{2} - x^{2} - 12y - 6 = 0\).
Firstly, we moved the constant term \(-6\) to the right side of the equation, leading to:
\(2y^{2} - x^{2} - 12y - 6 = 0\).
Firstly, we moved the constant term \(-6\) to the right side of the equation, leading to:
- \(2y^{2} - 12y - x^{2} = 6\)
- \(2(y^{2} - 6y) - x^{2} = 6\)
- \(2((y - 3)^{2} - 9) - x^{2} = 6\)
- \((y - 3)^2 - \frac{x^2}{2} = 12\)
Standard Form of a Hyperbola
The standard form of a hyperbola helps in easily identifying its properties, such as the center, axes orientation, and direction of opening. Once the equation is simplified through completing the square, it’s expressed as:
\[ \frac{x^2}{24} - \frac{(y - 3)^2}{12} = 1 \]Here is how we transition to this form from the completed square step.
After completing the square, we added 18 on both sides to isolate the squared terms, leading to:
\[ \frac{x^2}{24} - \frac{(y - 3)^2}{12} = 1 \]Here is how we transition to this form from the completed square step.
After completing the square, we added 18 on both sides to isolate the squared terms, leading to:
- \(2(y - 3)^2 - x^2 = 24\)
- \(\frac{x^2}{24} - \frac{(y - 3)^2}{12} = 1\)
Vertices and Foci of a Hyperbola
Understanding the vertices and foci of a hyperbola is crucial in sketching its graph, as these points define its shape and orientation.
Vertices are determined from the standard form. For the equation:
\[ \frac{x^2}{24} - \frac{(y - 3)^2}{12} = 1 \]The vertices lie along the transverse axis and are given by \((0, 3 \pm \sqrt{12})\) start here calculation explanation:
Vertices are determined from the standard form. For the equation:
\[ \frac{x^2}{24} - \frac{(y - 3)^2}{12} = 1 \]The vertices lie along the transverse axis and are given by \((0, 3 \pm \sqrt{12})\) start here calculation explanation:
- \(\sqrt{12} = 2\sqrt{3} \), hence vertices are \((0, 3 \pm 2\sqrt{3})\)
- \(c^2 = 24 + 12 = 36\)
- \(c = 6\), so foci are located at \((\pm 6, 3)\)