Chapter 8: Problem 51
For the following exercises, use the given information about the graph of each ellipse to determine its equation. Center (-3,4)\(;\) vertex (1,4)\(;\) one focus: \((-3+2 \sqrt{3}, 4)\)
Short Answer
Expert verified
The equation of the ellipse is \(\frac{(x+3)^2}{16} + \frac{(y-4)^2}{4} = 1\).
Step by step solution
01
Identify Ellipse Type
The given center - Center: (-3, 4) - Vertex: (1, 4) - Focus: (\(-3+2 \sqrt{3}, 4\)) indicates the ellipse is horizontal since both vertex and foci are horizontally aligned with the same y-coordinate.
02
Calculate the Distance to Vertex (Semi-major Axis)
The distance from the center to the vertex - Center: (-3, 4) - Vertex: (1, 4)Calculated as follows:\[a = |x_2 - x_1| = |1 - (-3)| = 4\] Hence, the semi-major axis length is 4.
03
Calculate the Distance to Focus (Determine 'c')
The distance from the center to the focus - Center: (-3, 4) - Focus: \((-3 + 2\sqrt{3}, 4)\)Can be calculated as:\[c = |-3 + 2\sqrt{3} - (-3)| = 2\sqrt{3}\]This 'c' helps in calculating the semi-minor axis 'b' through the standard equation relationship.
04
Apply the Ellipse Relationship
For an ellipse, the relationship is given by the equation:\[a^2 = b^2 + c^2\]Substituting the known values:\[16 = b^2 + (2\sqrt{3})^2\]Solving for \(b^2\):\[b^2 = 16 - 4 \times 3 = 4\]Thus, \(b = 2\).
05
Formulate the Ellipse Equation
For a horizontal ellipse centered at \((-3, 4)\), the standard form of the equation is:\[\frac{(x+3)^2}{4^2} + \frac{(y-4)^2}{2^2} = 1\]Simplified, the equation becomes:\[\frac{(x+3)^2}{16} + \frac{(y-4)^2}{4} = 1\]
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Semi-major Axis
An ellipse's semi-major axis is the longest radius extending from its center to the ellipse's edge. This axis is crucial in determining an ellipse's shape. In our exercise, this is a horizontal ellipse centered at \((-3, 4)\), with a vertex at \((1, 4)\). The semi-major axis runs along the x-axis, given the y-coordinates are constant. To find this length, calculate the horizontal distance between the center and the vertex.
Here's how:
Here's how:
- Center: \((-3, 4)\)
- Vertex: \((1, 4)\)
- Distance calculation: \(a = |1 - (-3)| = 4\)
Semi-minor Axis
The semi-minor axis, typically shorter, complements the semi-major axis in defining the ellipse's size and shape. The length of the semi-minor axis can be derived using the ellipse equation relationship: \(a^2 = b^2 + c^2\). Given the semi-major axis \(a\) and distance to the focus \(c\), solve for the semi-minor axis \(b\).
Let's break it down:
Let's break it down:
- Semi-major axis: \(a = 4\)
- Focus calculation, \(c = 2\sqrt{3}\)
- Equation: \(16 = b^2 + (2\sqrt{3})^2\)
- Solve for \(b^2: b^2 = 16 - 12 = 4\)
- Semi-minor axis \(b: b = 2\)
Ellipse Center
The center of an ellipse is the midpoint around which the entire shape is symmetrically plotted. For our equation, the center is specified as \((-3, 4)\). This point is a reference and is integral for writing the ellipse equation in its standard form.
Understanding the center helps in graphing, as it:
Understanding the center helps in graphing, as it:
- Serves as a pivot point for both axes.
- Determines the ellipse's position on a coordinate plane.
Graphing Ellipses
Graphed ellipses form enclosed, symmetric shapes on a coordinate plane. To achieve this, one should follow accurate plotting based on center, semi-major axis, and semi-minor axis. Our elliptic equation \(\frac{(x+3)^2}{16} + \frac{(y-4)^2}{4} = 1\) is derived from a horizontal alignment, guided by the formula for ellipse equations.
Steps to graph:
Steps to graph:
- Identify the center at \((-3, 4)\).
- From the center, move 4 units right and left for the semi-major axis.
- Move 2 units up and down for the semi-minor axis.
- Sketch the symmetric, oval shape connecting these bounds.