Chapter 7: Problem 10
Find the center-radius form for each circle satisfying the given conditions. Center \((-2,5) ;\) radius 4
Short Answer
Expert verified
The equation is \((x + 2)^2 + (y - 5)^2 = 16\).
Step by step solution
01
Recall the Equation of a Circle
The standard equation of a circle in center-radius form is given by: \((x-h)^2 + (y-k)^2 = r^2\), where \((h, k)\) is the center and \(r\) is the radius.
02
Identify the Given Values
The center of the circle is given as \((-2, 5)\), so \(h = -2\) and \(k = 5\). The radius \(r\) is given as 4.
03
Substitute Values into the Equation
Substitute \(h = -2\), \(k = 5\), and \(r = 4\) into the standard circle equation \((x-h)^2 + (y-k)^2 = r^2\). This gives us: \((x + 2)^2 + (y - 5)^2 = 4^2\).
04
Simplify the Radius Term
Calculate \(4^2\) to find the square of the radius: \(4^2 = 16\).
05
Write the Final Equation
Replace \(4^2\) with 16 in the equation from Step 3 to get the final center-radius form: \((x + 2)^2 + (y - 5)^2 = 16\).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Standard Equation of a Circle
The standard equation of a circle is a fundamental concept in geometry that provides a simple way to represent all the points making up a circle on a coordinate plane. This equation is written as: \[ (x-h)^2 + (y-k)^2 = r^2 \] Here:
- \((h, k)\) represents the center of the circle. These are the coordinates where the circle is perfectly balanced, much like the center of a wheel.
- \(r\) is the radius of the circle. It's the constant distance from the center to any point on the circle's edge.
Identify Circle Center and Radius
To use the standard equation of a circle, it's crucial to first identify the circle’s center and radius. In our exercise, the center of the circle was given as \((-2, 5)\). Here, the values \(h = -2\) and \(k = 5\) directly identify the circle's position.
- Center \((h, k)\): The coordinates \((-2, 5)\) tell us exactly where this circle is situated on the coordinate plane. The first number, \(-2\), is the \(x\)-coordinate, indicating it is to the left of the y-axis. The second number, \(5\), is the \(y\)-coordinate, showing it is above the x-axis.
- Radius \(r\): The radius is given as \(4\). This tells us how far the circle stretches from its center in any direction.
Substitute Values into Equation
After identifying the center \((-2, 5)\) and the radius \(4\), the next step is to substitute these values into our standard circle equation \[(x-h)^2 + (y-k)^2 = r^2\]. Here's how it looks:
- Replace \(h\) with \(-2\). Since subtracting a negative is equivalent to adding, the term becomes \((x + 2)^2\).
- Replace \(k\) with \(5\). This gives us \((y - 5)^2\).
- Replace \(r\) with \(4\). So \(r^2\) becomes \(4^2\), simplifying further to \(16\).