Chapter 11: Problem 36
Use a graphing device to graph the conic. $$4 x^{2}+9 y^{2}-36 y=0$$
Short Answer
Expert verified
Graph it as an ellipse centered at (0, 2) with axes lengths 6 and 4.
Step by step solution
01
Identify the Conic Equation
The given equation is \(4x^2 + 9y^2 - 36y = 0\). This equation can be identified as a conic section because it involves both \(x^2\) and \(y^2\) terms, suggesting it is either a circle, ellipse, hyperbola, or parabola.
02
Rearrange the Equation
First, rearrange the terms of the equation to group \(y\) terms together. The equation can be rewritten as \(4x^2 + 9(y^2 - 4y) = 0\).
03
Complete the Square
To convert the \(y\) terms into a perfect square, complete the square in \(y^2 - 4y\). \(y^2 - 4y\) can be rewritten as \((y-2)^2 - 4\). Thus, the equation becomes \(4x^2 + 9((y-2)^2 - 4) = 0\).
04
Simplify the Equation
Distribute the \(9\) into the completed square form:\(4x^2 + 9(y-2)^2 - 36 = 0\). Then add \(36\) to both sides to simplify:\(4x^2 + 9(y-2)^2 = 36\).
05
Divide by 36
Divide the entire equation by 36 to get it into standard form:\(\frac{x^2}{9} + \frac{(y-2)^2}{4} = 1\). This is the equation of an ellipse.
06
Identify the Ellipse's Properties
The equation \(\frac{x^2}{9} + \frac{(y-2)^2}{4} = 1\) represents an ellipse centered at (0, 2). It has a semi-major axis length of 3 (since \(\sqrt{9} = 3\)), aligned with the x-axis, and a semi-minor axis length of 2 (since \(\sqrt{4} = 2\)), along the y-axis.
07
Graph the Ellipse
Use a graphing device to plot the ellipse. Draw the ellipse centered at (0, 2) with a width along the x-axis of 6 units (2 × 3) and height along the y-axis of 4 units (2 × 2). Ensure proper labeling of axes and key points such as the center.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Conic Sections
Conic sections are curves obtained by intersecting a plane with a double-napped cone. They have four distinct types: circles, ellipses, parabolas, and hyperbolas, each with unique characteristics.
- A circle is formed when the intersecting plane is perpendicular to the cone's axis and does not pass through the apex. It appears as a perfectly round shape.
- An ellipse occurs when the intersecting plane is tilted, but not enough to become parallel to the edge of the cone. This results in an elongated circle.
- A parabola is created when the intersecting plane is parallel to the edge of the cone, forming a U-shaped curve.
- A hyperbola emerges when the intersecting plane intersects both nappes of the cone, resulting in two separate curves.
Completing the Square
Completing the square is a technique used to simplify quadratic expressions and equations, making them easier to solve or graph. This process transforms expressions into a perfect square trinomial, which is easier to manipulate. In our exercise, we focus on completing the square for the terms involving y:
- Start with the expression \(y^2 - 4y\).
- To complete the square, we add and subtract the square of half the coefficient of y inside the expression. This results in \((y - 2)^2 - 4\).
Graphing Conics
Graphing curves derived from conic sections, like ellipses, involves understanding their equations and properties. Ellipses have distinctive features that are critical for accurate graphing:
- The center of the ellipse provides a reference point for positioning the curve on a coordinate plane.
- Axes lengths—semi-major and semi-minor—determine the shape and orientation of the ellipse.
- The semi-major axis is the longest radius and the semi-minor axis is the shortest radii of the ellipse.
- The center is at \((0, 2)\).
- The semi-major axis is aligned along the x-axis with a length of 3 (\(\sqrt{9} = 3\)).
- The semi-minor axis lies along the y-axis with a length of 2 (\(\sqrt{4} = 2\)).
Standard Form of Ellipse
The standard form of an ellipse's equation is useful for identifying its key attributes easily. The standard form is \(\frac{(x-h)^2}{a^2} + \frac{(y-k)^2}{b^2} = 1\), where
- \((h, k)\) are the coordinates of the center.
- \(a^2\) and \(b^2\) represent the squares of the semi-major and semi-minor axes lengths, respectively.