Chapter 13: Problem 26
The graph of each equation is a circle. Find the center and the radius, and then graph the circle. See Examples 5 through 7. $$ x^{2}+y^{2}+6 x-4 y=3 $$
Short Answer
Expert verified
Center: (-3, 2), Radius: 4.
Step by step solution
01
Rearrange the Equation
The given equation is \( x^2 + y^2 + 6x - 4y = 3 \). First, we need to rearrange the terms so that all terms involving \( x \) are together, and all terms involving \( y \) are together. Thus, rewrite the equation as \( x^2 + 6x + y^2 - 4y = 3 \).
02
Complete the Square for the x-Terms
To complete the square for the \( x \) terms, take the coefficient of \( x \), which is 6, divide it by 2 to get 3, and then square it to get 9. Add and subtract 9 within the equation, resulting in \( x^2 + 6x + 9 - 9 + y^2 - 4y = 3 \).
03
Complete the Square for the y-Terms
To complete the square for the \( y \) terms, take the coefficient of \( y \), which is -4, divide it by 2 to get -2, and then square it to get 4. Add and subtract 4 within the equation, resulting in \( x^2 + 6x + 9 + y^2 - 4y + 4 = 3 + 9 + 4 \).
04
Write the Equation in Standard Form
The equation now is \( (x^2 + 6x + 9) + (y^2 - 4y + 4) = 16 \), which can be rewritten using the completed squares: \((x+3)^2 + (y-2)^2 = 16 \).
05
Identify the Center and Radius
The circle's equation is in the standard form \((x-h)^2 + (y-k)^2 = r^2 \). By comparing, we find that the center is \((-3, 2)\), and the radius is \( \sqrt{16} = 4 \).
06
Graph the Circle
Plot the center of the circle at \((-3, 2)\) on the Cartesian plane. From this point, draw a circle with a radius of 4 units. Ensure the circle is symmetrically around the center.
Unlock Step-by-Step Solutions & Ace Your Exams!
-
Full Textbook Solutions
Get detailed explanations and key concepts
-
Unlimited Al creation
Al flashcards, explanations, exams and more...
-
Ads-free access
To over 500 millions flashcards
-
Money-back guarantee
We refund you if you fail your exam.
Over 30 million students worldwide already upgrade their learning with 91Ó°ÊÓ!
Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Completing the Square
Completing the square is a helpful algebraic technique used to transform certain quadratic expressions into a form that is easier to work with. In the context of circles, this technique aids in rewriting the circle equation into its standard form. Here's a simple way to understand it:
- Take the term involving the linear variable (for example, if you have \(x^2 + 6x\), focus on the \(6x\)).
- Divide the coefficient of the variable by 2, and then square it. Here, \(6/2 = 3\) and \(3^2 = 9\). Add and subtract this square within the expression.
- This allows you to restructure the quadratic and linear terms into a perfect square trinomial, \((x+3)^2\) in our example after completing the square.
Standard Form of a Circle
The standard form of a circle's equation is an essential format for understanding the geometric properties of a circle. It is expressed as \((x-h)^2 + (y-k)^2 = r^2\), where:
- \( (h, k) \) is the center of the circle.
- \( r \) is the radius.
- The center \((h, k)\) is \((-3, 2)\).
- The radius \(r\) is \(4\), once you take the square root of 16.
Graphing Circles
Graphing a circle is a straightforward process once you have its equation in standard form. Here's how you can do it effectively:
- Identify the center \((h, k)\) from the equation \((x-h)^2 + (y-k)^2 = r^2\). This is the point around which your circle is centered. In our case, it's \((-3, 2)\).
- Determine the circle's radius \(r\). It's the square root of the number on the right side of the equation. Here it's \(4\), which means the circle extends 4 units from the center in all directions.
- Place the center at \((-3, 2)\) on a Cartesian plane.
- From the center, mark points 4 units away, horizontally and vertically. These define the edges of your circle.
- Draw a smooth round curve connecting these points. This represents all points equidistant from the center, forming the circle.