Chapter 2: Problem 52
Find the center and radius of the circle with the given equation. $$x^{2}+y^{2}-10 x+18=0$$
Short Answer
Expert verified
Center: (5, 0); Radius: \(\sqrt{7}\).
Step by step solution
01
Rearrange the equation
Start by rearranging the given equation to group the terms involving the same variable. Rewrite it as:\[ \left( x^{2} - 10x \right) + y^{2} = -18 \] This allows us to focus on completing the square for the terms involving \(x\).
02
Complete the square for x
To complete the square for \(x^2 - 10x\), take half of the coefficient of \(x\), which is \(-10\), divide by 2 to get \(-5\), and then square it to get \(25\). Add and subtract \(25\) inside the equation:\[ \left( x^{2} - 10x + 25 - 25 \right) + y^{2} = -18 \]This helps to form a perfect square trinomial for \(x\).
03
Simplify the equation
Rewrite the equation from Step 2 by recognizing the perfect square trinomial:\[ \left( x - 5 \right)^{2} - 25 + y^{2} = -18 \]Now add 25 to both sides to balance the equation:\[ \left( x - 5 \right)^{2} + y^{2} = 7 \]
04
Identify the center and radius
The standard form of a circle's equation is \((x - h)^2 + (y - k)^2 = r^2\), where \((h, k)\) is the center and \(r\) is the radius. From the equation \( (x - 5)^2 + y^2 = 7 \), the center is \((5, 0)\) and the radius is \(\sqrt{7}\).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Completing the Square
When working with quadratic equations, completing the square is a valuable method to rearrange terms into a perfect square trinomial. This technique is especially useful when dealing with circle equations. Completing the square involves:
- Taking the coefficient of the linear term (in our case, \(-10\) from \(x^2 - 10x\))
- Dividing this coefficient by 2 to find the midpoint
- Squaring the result to ensure we can form a perfect square
Center of a Circle
Finding the center of a circle is crucial for understanding its position on the coordinate plane. The center is defined from the circle's standard equation: \((x - h)^2 + (y - k)^2 = r^2\).
The terms \(h\) and \(k\) indicate the horizontal and vertical shifts from the origin, respectively.
In our example, from the equation \((x - 5)^2 + y^2 = 7\), we identify the center as \( (5, 0) \).
The terms \(h\) and \(k\) indicate the horizontal and vertical shifts from the origin, respectively.
In our example, from the equation \((x - 5)^2 + y^2 = 7\), we identify the center as \( (5, 0) \).
- \((h, k) = (5, 0)\): The circle is shifted 5 units to the right from the origin and remains on the x-axis since the y term wasn't shifted.
Radius of a Circle
The radius of a circle is the distance from its center to any point on the circumference. Having the standard equation format makes identifying this straightforward.
The radius is derived from the equation: \((x - h)^2 + (y - k)^2 = r^2\), where \(r^2\) is the number on the right side.
From \((x - 5)^2 + y^2 = 7\), the radius \(r\) is the square root of 7.
The radius is derived from the equation: \((x - h)^2 + (y - k)^2 = r^2\), where \(r^2\) is the number on the right side.
From \((x - 5)^2 + y^2 = 7\), the radius \(r\) is the square root of 7.
- Radius \( r = \sqrt{7} \): This is approximately 2.65, giving the length of each line segment from the center \((5, 0)\) to any point on the circle's boundary.
Standard Form of a Circle
The standard form of a circle’s equation is fundamental in identifying its geometric properties like center and radius. This form is expressed as: \((x - h)^2 + (y - k)^2 = r^2\), providing a clear view of:
Recognizing the standard form supports solving more complex problems, graphing circles, and translating equations into meaningful geometric insights.
- \((h, k)\): The circle’s center coordinates.
- \(r\): The radius length.
Recognizing the standard form supports solving more complex problems, graphing circles, and translating equations into meaningful geometric insights.