Chapter 7: Problem 67
Solve the system of equations. Give graphical support by making a sketch. $$\begin{aligned} &4 x^{2}+16 y^{2}=64\\\ &x^{2}+y^{2}=9 \end{aligned} $$
Short Answer
Expert verified
The system has four intersection points: \(\left(\pm\sqrt{\dfrac{20}{3}}, \pm\sqrt{\dfrac{7}{3}}\right)\).
Step by step solution
01
Analyze the First Equation
The first equation is \(4x^2 + 16y^2 = 64\). Divide every term by 64 to rewrite it in the form \(\dfrac{x^2}{16} + \dfrac{y^2}{4} = 1\). This represents an ellipse centered at the origin with semi-major axis 4 along the x-axis and semi-minor axis 2 along the y-axis.
02
Analyze the Second Equation
The second equation is \(x^2 + y^2 = 9\), which is a circle centered at the origin with a radius of 3.
03
Sketch the Graphs
Draw the two conic sections on the same coordinate plane. The ellipse is wider horizontally, stretching from -4 to 4 on the x-axis and from -2 to 2 on the y-axis. The circle goes out to 3 units in all directions from the origin. The points where these two graphs intersect are the solutions to the system of equations.
04
Find the Intersection Points
Substitute \(x^2 = 9 - y^2\) from the circle's equation into the ellipse's equation, yielding \(4(9-y^2) + 16y^2 = 64\). Simplifying, you get \(36 + 12y^2 = 64\), leading to \(12y^2 = 28\) or \(y^2 = \dfrac{7}{3}\). Solving for \(x^2\), get \(x^2 = 9 - \dfrac{7}{3} = \dfrac{20}{3}\).
05
Calculate Valid Points
The possible combinations of solutions for \(x\) and \(y\) can be found by solving separately for each combination of \(\pm\sqrt{\dfrac{20}{3}}\) and \(\pm\sqrt{\dfrac{7}{3}}\). Hence the four points of intersection on the graph are \(\left( \sqrt{\dfrac{20}{3}}, \sqrt{\dfrac{7}{3}} \right)\), \(\left( -\sqrt{\dfrac{20}{3}}, \sqrt{\dfrac{7}{3}} \right)\), \(\left( \sqrt{\dfrac{20}{3}}, -\sqrt{\dfrac{7}{3}} \right)\), and \(\left( -\sqrt{\dfrac{20}{3}}, -\sqrt{\dfrac{7}{3}} \right)\).
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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 shape that looks like a flattened circle. In mathematics, an ellipse can be defined by the equation \(\frac{x^2}{a^2} + \frac{y^2}{b^2} = 1\). This equation represents an ellipse centered at the origin
- \(a\) is the length of the semi-major axis, which is the longest diameter of the ellipse.
- \(b\) is the length of the semi-minor axis, the shortest diameter of the ellipse.
Circle
A circle is a simple shape and is very symmetrical. It is defined in a plane by the equation \(x^2 + y^2 = r^2\), where \(r\) is the radius of the circle. This shape retains consistent distance \(r\) from a central point at all angles.
- The radius \(r\) is the distance from the center of the circle to any point on the circumference.
Intersection Points
Finding the intersection points of a system of equations involves locating the coordinates where two or more graphs cross. These intersection points are the solutions to the system. When dealing with equations like an ellipse and a circle, we substitute and solve to find where they meet
- Solving the system starts by expressing one variable in terms of the other using one of the equations.
- Substituting this expression into the second equation allows solving a single equation with one variable.
Graphical Solution
A graphical solution involves solving equations by drawing them on a coordinate plane and identifying where they intersect. For systems of equations, this method is particularly useful as it offers a visual representation of how the equations relate to each other.
- Each equation is represented as a curve or a line on the graph.
- By plotting these equations, we can see where their paths cross.