Chapter 11: Problem 108
Determine the center and radius of the circle \(x^{2}-10 x+y^{2}+2 y=0\)
Short Answer
Expert verified
The center is (5, -1) and the radius is \sqrt{26}.
Step by step solution
01
- Rewrite the Equation in Standard Circle Form
The given equation is: \[ x^{2} - 10x + y^{2} + 2y = 0 \]. To find the center and radius, rewrite this equation in the standard form of a circle equation: \[ (x-h)^{2} + (y-k)^{2} = r^{2} \].
02
- Complete the Square for the x Terms
Take the x terms \[ x^{2} - 10x \]. To complete the square, add and subtract \[ \frac{(-10)^2}{4} = 25 \]: \[ x^{2} - 10x + 25 - 25 \]. This can be rewritten as: \[ (x - 5)^{2} - 25 \].
03
- Complete the Square for the y Terms
Now take the y terms \[ y^{2} + 2y \]. To complete the square, add and subtract \[ \frac{2^2}{4} = 1 \]: \[ y^{2} + 2y + 1 - 1 \]. This can be rewritten as: \[ (y + 1)^{2} - 1 \].
04
- Rewrite the Equation with Completed Squares
Combine the results from Steps 2 and 3 into the original equation: \[ (x - 5)^{2} - 25 + (y + 1)^{2} - 1 = 0 \].
05
- Simplify the Equation
Simplify the equation by moving constants to the other side: \[ (x - 5)^{2} + (y + 1)^{2} - 25 - 1 = 0 \] \[ (x - 5)^{2} + (y + 1)^{2} = 26 \]. This is now in the form \[ (x-h)^{2} + (y-k)^{2} = r^{2} \].
06
- Identify the Center and Radius
From the simplified equation \[ (x - 5)^{2} + (y + 1)^{2} = 26 \], identify the center \[(h, k) = (5, -1)\] and the radius \( r = \sqrt{26} \).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
center of a circle
To find the center of a circle from its equation, you need to put the equation into its standard form. This form is: ewline (x-h)^2 + (y-k)^2 = r^2 ewline where (h,k) represents the center of the circle. ewline Steps to identify the center: ewline
- Identify the x-terms and complete the square.
- Identify the y-terms and complete the square.
- Combine these completed squares into one equation.
- The values of h and k from the resulting equation will give you the coordinates of the center of the circle.
radius of a circle
The radius of a circle in the standard equation form ewline (x-h)^2 + (y-k)^2 = r^2 ewline is represented by r. ewline To find the radius:
- First, complete the square for both x and y terms to get the equation in standard form.
- Identify the value on the right-hand side of the equation, which is r^2.
- Take the square root of this value to get the radius, r.
completing the square
Completing the square is a method used to transform quadratic equations into a form that allows easy identification of key properties. ewline Steps to complete the square:
- For the x terms, take the coefficient of x, divide it by 2, and square it.
- Add and subtract this squared value within the equation.
- Rewrite the expression as a squared binomial.
- Repeat the same process for the y terms.
- Identify the coefficient of x, which is -10.
- Divide by 2 to get -5, then square it to get 25.
- Add and subtract 25 inside the equation: x^2 - 10x + 25 - 25
- Rewrite as (x-5)^2 - 25
- Identify 2, divide by 2 to get 1, then square it to get 1.
- Add and subtract 1: y^2 + 2y + 1 - 1
- Rewrite as (y+1)^2 - 1