Chapter 8: Problem 40
For the following exercises, sketch a graph of the hyperbola, labeling vertices and foci. $$ -x^{2}+8 x+4 y^{2}-40 y+88=0 $$
Short Answer
Expert verified
Vertices: (2, 5) and (6, 5). Foci: (4±√5, 5).
Step by step solution
01
Rewrite the Equation
First, let's rewrite the given equation by grouping the terms related to \(x\) and \(y\). The given equation is:\[-x^2 + 8x + 4y^2 - 40y + 88 = 0\]We'll rearrange it as:\[-(x^2 - 8x) + 4(y^2 - 10y) = -88\].
02
Complete the Square
Next, we complete the square for both the \(x\) and \(y\) terms. For \(-x^2 + 8x\): Complete the square:\[-(x^2 - 8x + 16 - 16) = -(x^2 - 8x + 16) + 16 = -(x-4)^2 + 16\].For \(4y^2 - 40y\):Factor out the 4:\[4(y^2 - 10y + 25 - 25) = 4((y-5)^2 - 25) = 4(y-5)^2 - 100\].
03
Redefine the Equation
Now substitute the completed square forms back into the equation:\[-(x-4)^2 + 16 + 4(y-5)^2 - 100 = -88\].Simplify the constant terms:\[-(x-4)^2 + 4(y-5)^2 - 84 = -88\]\[-(x-4)^2 + 4(y-5)^2 = -4\].
04
Divide to Simplify
Divide through by -4 to express the equation in the form of a hyperbola:\[\frac{(x-4)^2}{4} - (y-5)^2 = 1\].This can be rewritten as:\[\frac{(x-4)^2}{4} - \frac{(y-5)^2}{1} = 1\].
05
Identify the Hyperbola Features
From the equation \[\frac{(x-4)^2}{4} - \frac{(y-5)^2}{1} = 1\], we can identify the hyperbola's features:- Center: \((h, k) = (4, 5)\).- Vertices: Since \(a^2 = 4\), we have \(a = 2\), so vertices are at \((4±2, 5)\) or \((2, 5)\) and \((6, 5)\).- Foci: Calculate using \(c = \sqrt{a^2 + b^2} = \sqrt{4 + 1} = \sqrt{5}\), so foci are \((4±\sqrt{5}, 5)\).
06
Sketch the Hyperbola
With the center \((4, 5)\), vertices \((2, 5)\) and \((6, 5)\), and foci \((4±\sqrt{5}, 5)\), sketch the horizontal hyperbola on a graph.- Draw the transverse axis through the vertices.- Mark the vertices and foci on the graph.- Sketch the asymptotes, which depend on slopes derived from \(b/a = 1/2\), passing through the center.- Draw the hyperbola approaching these asymptotes.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Completing the Square
Completing the square is a technique used to transform a quadratic expression into a perfect square trinomial. This helps in rewriting a hyperbola equation so it's easier to understand the structure and characteristics of the hyperbola.
To complete the square, you need to follow these steps for each of the variable terms:
To complete the square, you need to follow these steps for each of the variable terms:
- Identify the coefficient of the linear term.
- Divide this coefficient by 2.
- Square the result.
- Add and subtract this square inside the equation to maintain the equality.
- Linear coefficient is \(8\).
- Half of it is \(4\), and its square is \(16\).
- Rewrite as \(x^2 - 8x + 16 - 16\).
- This simplifies to \((x-4)^2 - 16\).
Vertices of Hyperbola
Vertices of a hyperbola are key points that help define its shape, located on the major axis of the hyperbola. Given a hyperbola in the standard form, vertices are determined by the values of \(a\) (the distance from the center to a vertex on the transverse axis).
- For a horizontal hyperbola \(\frac{(x-h)^2}{a^2} - \frac{(y-k)^2}{b^2} = 1\), vertices are \((h\pm a, k)\).
- For the given equation, \(a^2 = 4\), so \(a = 2\).
- With the center at \((4,5)\), vertices are \((4\pm2, 5) = (2, 5)\) and \((6, 5)\).
Foci of Hyperbola
The foci (plural of focus) are two points inside each branch of a hyperbola. They are crucial for defining the nature of hyperbolas, influencing their width and openness. The distance from the center to each focus is \(c\), calculated using the relationship \(c = \sqrt{a^2 + b^2}\).
- For \(a^2 = 4\) and \(b^2 = 1\), \(c = \sqrt{4 + 1} = \sqrt{5}\).
- For the equation \({\frac{(x-4)^2}{4} - \frac{(y-5)^2}{1} = 1}\), foci reside on the transverse axis.
- Thus, the foci are at \( (h\pm\sqrt{5}, k)\), or \((4\pm\sqrt{5}, 5)\).
Center of Hyperbola
The center of a hyperbola is a critical point from which the hyperbola is symmetrically stretched. It is akin to the midpoint between its vertices and foci.
- The general form of a hyperbola's equation reveals the center \((h, k)\) from the quadratic components' completed square format.
- In this hyperbola, transformed to \({\frac{(x-4)^2}{4} - \frac{(y-5)^2}{1} = 1}\), the center is clearly \((4,5)\).