Chapter 12: Problem 33
Write the center-radius form of the circle with the given equation. Give the center and radius. $$3 x^{2}+3 y^{2}-12 x-24 y+12=0$$
Short Answer
Expert verified
Center: (2, 4) and Radius: 4
Step by step solution
01
- Factor out common factor
Start by factoring out the common factor of 3 from the given equation: \[3(x^2 + y^2 - 4x - 8y + 4) = 0\] Divide both sides of the equation by 3:\[x^2 + y^2 - 4x - 8y + 4 = 0\]
02
- Move constant term to the other side
Isolate the constant term by moving it to the other side of the equation: \[x^2 + y^2 - 4x - 8y = -4\]
03
- Complete the square for the x-terms
Complete the square for the x-terms: \[x^2 - 4x \] To do this, take half of the coefficient of x, square it, and add it to both sides of the equation. Half of -4 is -2, and (-2)^2 is 4. So add 4 to both sides: \[x^2 - 4x + 4 + y^2 - 8y = -4 + 4\]Which simplifies to:\[(x - 2)^2 + y^2 - 8y = 0\]
04
- Complete the square for the y-terms
Complete the square for the y-terms: \[y^2 - 8y\] To do this, take half of the coefficient of y, square it, and add it to both sides of the equation. Half of -8 is -4, and (-4)^2 is 16. So add 16 to both sides: \[(x - 2)^2 + y^2 - 8y + 16 = 0 + 16\]Which simplifies to: \[(x - 2)^2 + (y - 4)^2 = 16\]
05
- Write the center-radius form and determine the center and radius
The equation is now in the center-radius form: \[(x - 2)^2 + (y - 4)^2 = 16\] Identify the center \(h, k\) and the radius \(r\):The center is (2, 4) and the radius is \sqrt{16} = 4\.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
center-radius form
The center-radius form of a circle is a simple way to write the equation of a circle. This form is very useful in geometry and algebra because it clearly shows the center and the radius of the circle. The general equation for the center-radius form of a circle is:
\[ (x-h)^{2} + (y-k)^{2} = r^{2} \]
Here:
\[ (x-h)^{2} + (y-k)^{2} = r^{2} \]
Here:
- \
completing the square
Completing the square is an algebraic technique used to transform a quadratic equation into a perfect square trinomial, making the equation easier to solve or interpret. It is especially useful when converting the general form of a circle's equation to the center-radius form. To complete the square for a quadratic in the form \(ax^2 + bx + c\), follow these steps:
- Step 1: Rearrange the equation to group the x-terms and y-terms on one side and the constant on the other side.
- Step 2: For each group, take half of the linear coefficient (the number attached to x or y), square it, and add this square to both sides of the equation.
- Step 3: Rewrite the quadratic expressions as perfect squares.
geometry
Understanding the circle's equation through geometry can help visualize its properties. A circle is defined as the set of all points in a plane that are the same distance (the radius) from a fixed point (the center).
In a coordinate plane, the equation of a circle reveals key geometric features:
In a coordinate plane, the equation of a circle reveals key geometric features:
- The center, \((h, k)\), is the fixed point from which all points on the circle are equally distant.
- The radius, \(r\), is the constant distance from the center to any point on the circle.
radius calculation
Calculating the radius from the equation of a circle involves recognizing the squared term on the right-hand side of the center-radius form. The radius is derived from this term, as it represents the squared value of the radius.
For instance, in the equation \((x-2)^2 + (y-4)^2 = 16\), the number \(16\) is the square of the radius. To find the radius, take the square root of \(16\), which gives us:
For instance, in the equation \((x-2)^2 + (y-4)^2 = 16\), the number \(16\) is the square of the radius. To find the radius, take the square root of \(16\), which gives us:
- \(r = \sqrt{16} = 4\)