Chapter 12: Problem 43
Rewrite each equation in the standard form for the equation of a circle, and identify its center and radius. $$x^{2}-3 x+y^{2}-y=1$$
Short Answer
Expert verified
Center: \( \left( \frac{3}{2}, \frac{1}{2} \right) \), Radius: \( \sqrt{\frac{7}{2}} \)
Step by step solution
01
- Group x and y terms
Rewrite the equation by grouping the x terms and y terms together: \[x^2 - 3x + y^2 - y = 1\]
02
- Complete the square for x terms
To complete the square for the x terms, take the coefficient of \(x\) (which is -3), divide by 2, and then square it: \[\left( \frac{-3}{2} \right)^2 = \left(\frac{-3}{2}\right)^2 = \frac{9}{4}\]Add and subtract \(\frac{9}{4}\) inside the equation:\[x^2 - 3x + \frac{9}{4} + y^2 - y = 1 + \frac{9}{4}\]
03
- Complete the square for y terms
Similarly, to complete the square for the y terms, take the coefficient of \(y\) (which is -1), divide by 2, and then square it:\[\left(\frac{-1}{2}\right)^2 = \left(\frac{-1}{2}\right)^2 = \frac{1}{4}\]Add and subtract \(\frac{1}{4}\) inside the equation:\[x^2 - 3x + \frac{9}{4} + y^2 - y + \frac{1}{4} = 1 + \frac{9}{4} + \frac{1}{4}\]
04
- Simplify and rearrange the equation
Combine and simplify the equation:\[\left( x - \frac{3}{2} \right)^2 + \left( y - \frac{1}{2} \right)^2 = \frac{14}{4}\]Which simplifies to:\[\left( x - \frac{3}{2} \right)^2 + \left( y - \frac{1}{2} \right)^2 = \frac{7}{2}\]
05
- Identify center and radius
The equation is now in the standard form of a circle, \[(x-h)^2 + (y-k)^2 = r^2\]where the center \((h, k)\) is \( \left( \frac{3}{2}, \frac{1}{2} \right) \)and the radius r is \( r = \sqrt{\frac{7}{2}} \)
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
completing the square
Completing the square is a method used to convert a quadratic equation into a perfect square trinomial. This technique helps in transforming equations to make them easier to solve or analyze. For a quadratic term like \(x^2 - 3x\), you complete the square by following these steps:
Add and subtract this value inside the equation helps to create a perfect square trinomial. This transformation makes it possible to re-write the equation in a simpler and more recognizable form.
Now do the same with the \(y\) terms as seen in the solution.
- Take the coefficient of x (which is -3), divide by 2 to get \(-\frac{3}{2}\)
- Square the result to get \(\left(\frac{-3}{2}\right)^2 = \frac{9}{4}\)
Add and subtract this value inside the equation helps to create a perfect square trinomial. This transformation makes it possible to re-write the equation in a simpler and more recognizable form.
Now do the same with the \(y\) terms as seen in the solution.
center of a circle
The center of a circle in the standard form of the circle's equation \((x-h)^2 + (y-k)^2 = r^2 \) is the point \( (h, k) \). This form makes it straightforward to identify the circle's center by simply looking at the values \(h\) and \(k\).
Using our example:
\((x-\frac{3}{2})^2 + (y-\frac{1}{2})^2 = \frac{7}{2} \),
we can see that the coordinates of the center are \left( \frac{3}{2}, \frac{1}{2} \right)\.
Using our example:
\((x-\frac{3}{2})^2 + (y-\frac{1}{2})^2 = \frac{7}{2} \),
we can see that the coordinates of the center are \left( \frac{3}{2}, \frac{1}{2} \right)\.
radius of a circle
The radius of a circle is the distance from the center to any point on the circle. In the standard form equation of a circle, \((x-h)^2 + (y-k)^2 = r^2\), \( r^2 \) represents the square of the circle's radius. To find the radius, take the square root of the constant term on the right side of the equation.
In our example:
\((x - \frac{3}{2})^2 + (y - \frac{1}{2})^2 = \frac{7}{2} \),
we identify \r^2 = \frac{7}{2}\.
Therefore, the radius \ r \ is \sqrt{\frac{7}{2}}\.
In our example:
\((x - \frac{3}{2})^2 + (y - \frac{1}{2})^2 = \frac{7}{2} \),
we identify \r^2 = \frac{7}{2}\.
Therefore, the radius \ r \ is \sqrt{\frac{7}{2}}\.
algebraic manipulation
Algebraic manipulation is the process of rearranging and simplifying equations using various algebraic techniques. When solving for the standard form of a circle equation, this involves:
Mastering algebraic manipulation techniques is crucial for solving a wide range of mathematical problems, including converting equations to standard forms like the circle equation we discussed here.
- Grouping terms with similar variables (x terms together and y terms together)
- Using methods like completing the square to transform parts of the equation into recognizable formats (perfect square trinomials in this context)
- Simplifying fractions and combining terms to reach the desired form
Mastering algebraic manipulation techniques is crucial for solving a wide range of mathematical problems, including converting equations to standard forms like the circle equation we discussed here.