Chapter 0: Problem 23
Plot the graph of each equation. Begin by checking for symmetries and be sure to find all \(x\) - and \(y\) -intercepts. \(2 x^{2}-4 x+3 y^{2}+12 y=-2\)
Short Answer
Expert verified
The graph is an ellipse centered at \((1, -2)\) with no real x-intercepts and y-intercepts at \((0, -0.175)\) and \((0, -3.825)\).
Step by step solution
01
Write the Equation in Standard Form
First, rearrange the given equation. The equation is given as \(2x^2 - 4x + 3y^2 + 12y = -2\). Move \(-2\) to the right side to isolate it, resulting in \(2x^2 - 4x + 3y^2 + 12y + 2 = 0\).
02
Complete the Square for the X Terms
Focus on the terms with \(x\): \(2x^2 - 4x\). Factor out a 2: \(2(x^2 - 2x)\). Complete the square inside the parentheses: \(x^2 - 2x = (x-1)^2 - 1\). The expression becomes \(2((x-1)^2 - 1)\), or \(2(x-1)^2 - 2\).
03
Complete the Square for the Y Terms
Turn to the terms with \(y\): \(3y^2 + 12y\). Factor out a 3: \(3(y^2 + 4y)\). Complete the square inside the parentheses: \(y^2 + 4y = (y+2)^2 - 4\). The expression becomes \(3((y+2)^2 - 4)\), or \(3(y+2)^2 - 12\).
04
Rewrite the Equation in Completed Square Form
Substitute the completed square expressions back into the modified equation: \(2(x-1)^2 - 2 + 3(y+2)^2 - 12 = 0\). Simplify to \(2(x-1)^2 + 3(y+2)^2 = 14\).
05
Identify the Type of Conic Section
Compare the simplified equation \(2(x-1)^2 + 3(y+2)^2 = 14\) with the standard form of an ellipse \(\frac{(x-h)^2}{a^2} + \frac{(y-k)^2}{b^2} = 1\). Divide the entire equation by 14: \(\frac{(x-1)^2}{7} + \frac{(y+2)^2}{\frac{14}{3}} = 1\), identifying it as an ellipse centered at \((1, -2)\).
06
Find the X-Intercepts
For \(x\)-intercepts, set \(y = 0\) in the equation: \(2x^2 - 4x + 3(0)^2 + 12(0) = -2\), which simplifies to \(2x^2 - 4x + 2 = 0\). Solve this quadratic using the quadratic formula: \(x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}\) with \(a=2, b=-4, c=2\). It yields no real roots as the discriminant is zero.
07
Find the Y-Intercepts
For \(y\)-intercepts, set \(x = 0\) in the equation: \(2(0)^2 - 4(0) + 3y^2 + 12y = -2\), which simplifies to \(3y^2 + 12y + 2 = 0\). Use the quadratic formula to solve for \(y\) with \(a=3, b=12, c=2\), giving two roots: \(y = -0.175\) and \(y = -3.825\).
08
Determine Symmetry
Check the symmetry of the ellipse. An ellipse is symmetric with respect to its axes and its center. Here, the center \((1, -2)\) confirms symmetry across the point.
09
Plot the Graph
Using the details above, plot the ellipse with the center at \((1, -2)\), axes aligned with the coordinate axes, semi-axis lengths \(\sqrt{7}\) along the x-axis and \(\sqrt{\frac{14}{3}}\) along the y-axis. Remember the y-intercepts are \((-0.175, y)\) and \((-3.825, y)\), with symmetry around the point \((1, -2)\).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Ellipse
An ellipse is a type of conic section that appears as an elongated circle. It comes from cutting through a cone at an angle, allowing two symmetric halves. The standard form of an ellipse equation is \[\frac{(x-h)^2}{a^2} + \frac{(y-k)^2}{b^2} = 1,\]where
- \((h, k)\) is the center of the ellipse.
- \(a\) and \(b\) are the semi-major and semi-minor axis lengths, corresponding to the ellipse's longest and shortest diameters.
Completing the Square
Completing the square is a valuable algebraic method used to rewrite quadratic equations into a form that reveals important properties like the vertex of a parabola or the center of an ellipse. The process involves transforming an expression like \(ax^2 + bx + c\) into \(a(x-h)^2 + k\). Here's how it's done:
- Focus on the quadratic and linear terms: For \(2x^2 - 4x\), first factor out the coefficient 2 to simplify: \(2(x^2 - 2x)\).
- Find a value that completes the square inside the parentheses \((x^2 - 2x + ?)\): reformat it into a perfect square form \((x-1)^2 - 1\). The number 1 here is derived by taking half of the linear coefficient \((-2/2 = -1)\) and squaring it.
- Repeat the process similarly for the \(y\) terms.
Intercepts
Intercepts are fundamental points where a graph meets the axes. These points provide a useful reference for sketching conic sections like ellipses. In this instance, intercepts are determined by setting one variable to zero and solving for the other.For x-intercepts, where \(y = 0\), we evaluate the equation:\[2x^2 - 4x + 2 = 0\]Using the quadratic formula reveals no real solutions, indicating no x-intercepts.For y-intercepts, where \(x = 0\), substitute into the original equation:\[3y^2 + 12y + 2 = 0\]Applying the quadratic formula yields two solutions: \(y = -0.175\) and \(y = -3.825\). These solutions represent the points at which the ellipse intersects the y-axis. Knowing intercepts assists in correctly placing the ellipse on the coordinate plane, confirming its orientation and exact location.