Chapter 2: Problem 31
Exer. \(23-34\) : Sketch the graph of the circle or semicircle. $$y=-\sqrt{16-x^{2}}$$
Short Answer
Expert verified
The graph is the lower half of a circle with radius 4 centered at (0,0).
Step by step solution
01
Recognize the Equation Form
The given equation is in the form of \( y = -\sqrt{16-x^2} \). This represents the lower half of a circle centered at the origin with a radius of 4, because \( y = \pm \sqrt{16-x^2} \) is the equation for a circle with radius 4 centered at (0,0) . The negative sign indicates the lower semicircle.
02
Identify the Radius and Center
The equation \( 16 - x^2 \) inside the square root implies that the circle is centered at \((0,0)\). The expression \( x^2 + y^2 = 16 \) is extracted from this, which is the equation of a circle with radius 4 centered at the origin.
03
Determine the Domain and Range
The domain of \( y = -\sqrt{16-x^2} \) is the set of \( x \) values for which the expression inside the square root is non-negative: \( -4 \leq x \leq 4 \). The range for \( y \) is from \(-4\) to \(0\) because \( y \) represents the negative values of the square root.
04
Plot Key Points
Determine key points on the graph. When \( x = 0 \), \( y = -4 \). At \( x = \pm 4 \), \( y = 0 \). These points (0,-4), (4,0), and (-4,0) help shape the semicircle graph.
05
Sketch the Graph
Using the center at (0,0) and radius 4, sketch the lower semicircle. Start from (-4,0) to (4,0) along the x-axis and draw the arc down to meet at (0,-4), completing the lower half of the circle.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Equation of a Circle
The equation of a circle is one of the fundamental concepts in geometry. A typical equation for a circle with a center at \( (h, k) \) and radius \( r \) is given by:
- \( (x - h)^2 + (y - k)^2 = r^2 \)
Domain and Range
Understanding the domain and range is crucial when graphing functions. The domain of a function is the complete set of possible values of the independent variable, which is \( x \) in this context. For the equation \( y = -\sqrt{16-x^2} \), the domain is determined by the values for which the expression under the square root is non-negative. \( 16-x^2 \) must be greater than or equal to zero, leading us to:
- \( -4 \leq x \leq 4 \)
- \( y: -4 \leq y \leq 0 \)
Center and Radius
A circle's center and radius give insight into its position and size. From the circle equation \( x^2 + y^2 = 16 \), we infer the circle is centered at the origin \( (0,0) \). This is because there are no additional constants added or subtracted from \( x \) or \( y \), which means both \( h \) and \( k \) are zero. The expression equates to the circle's bottom quadrant due to its negative square root. The radius is derived from the constant on the right-hand side of the circle equation, which is 16:
- Taking the square root yields a radius of \( 4 \).
Key Points on a Graph
Identifying key points is a stepping stone to accurately sketching graphs. For the semicircle \( y = -\sqrt{16-x^2} \), let's find the values that define its shape:
- When \( x = 0 \), \( y = -4 \). This is the lowest point of the semicircle.
- When \( x = 4 \), \( y = 0 \), marking the rightmost endpoint.
- When \( x = -4 \), \( y = 0 \), marking the leftmost endpoint.