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Ch. 2 - Functions and Graphs
Blitzer - College Algebra 8th Edition
Blitzer8th EditionCollege AlgebraISBN: 9780136970514Not the one you use?Change textbook
Chapter 3, Problem 41

Give the center and radius of the circle described by the equation and graph each equation. Use the graph to identify the relation's domain and range. x² + y² = 16

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Recognize that the given equation \(x^{2} + y^{2} = 16\) is the standard form of a circle centered at the origin, where the general form is \(\left(x - h\right)^{2} + \left(y - k\right)^{2} = r^{2}\) with center \((h, k)\) and radius \(r\).
Compare the given equation to the general form: since there are no \((x - h)\) or \((y - k)\) terms, the center is at \((0, 0)\).
Identify the radius by taking the square root of the constant on the right side: \(r = \sqrt{16}\).
To find the domain, consider all possible \(x\)-values for which \(y\) is real. Since \(y^{2} = 16 - x^{2}\), \(y\) is real only when \(16 - x^{2} \geq 0\), which implies \(-4 \leq x \leq 4\).
Similarly, for the range, consider all possible \(y\)-values. Since \(x^{2} = 16 - y^{2}\), \(x\) is real only when \(16 - y^{2} \geq 0\), which implies \(-4 \leq y \leq 4\).

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Equation of a Circle

The standard form of a circle's equation is (x - h)² + (y - k)² = r², where (h, k) is the center and r is the radius. In the given equation x² + y² = 16, the center is at the origin (0,0) and the radius is the square root of 16, which is 4.
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Graphing Circles

Graphing a circle involves plotting its center and using the radius to mark points in all directions. The circle is the set of all points equidistant from the center. For x² + y² = 16, plot the center at (0,0) and draw a circle passing through points 4 units away on the x- and y-axes.
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Domain and Range of a Circle

The domain of a circle is the set of all possible x-values, and the range is the set of all possible y-values. For the circle x² + y² = 16, the domain and range are both [-4, 4], since the radius limits the x and y values to within 4 units from the center.
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