Chapter 2: Problem 21
Sketch, on the same coordinate plane, the graphs of \(f\) for the given values of \(c\). (Make use of symmetry, shifting, stretching, compressing, or reflecting.) $$f(x)=c \sqrt{4-x^{2}}, \quad c=-2,1,3$$
Short Answer
Expert verified
Three semicircles with c affect stretch, compression, and reflection on the coordinate plane.
Step by step solution
01
Identify the base function
The base function is given by \( y = \sqrt{4-x^2} \). This represents a semicircle with a radius of 2 centered at the origin on the x-axis.
02
Understand transformations by c-values
The value of \( c \) will stretch or compress the graph vertically and can also reflect it across the x-axis if \( c \) is negative. For \( c = -2, 1, 3 \), this represents reflection and stretching/compressing for each \( c \).
03
Graph for c = 1
The function \( f(x) = \sqrt{4-x^2} \) is the semicircle from \( -2 \) to \( 2 \). It's already given for \( c = 1 \), so we plot the half-circle spanning from \(( -2, 0 )\) through \((0, 2)\) to \(( 2, 0 )\).
04
Graph for c = -2
For \( c = -2 \), we reflect the semicircle across the x-axis and stretch it vertically by a factor of 2. The new function is \( f(x) = -2 \sqrt{4-x^2} \). This new graph spans from \(( -2, 0 )\) down to \((0, -4)\) and back up to \(( 2, 0 )\).
05
Graph for c = 3
For \( c = 3 \), the semicircle is stretched vertically by a factor of 3 but is not reflected. The new function is \( f(x) = 3 \sqrt{4-x^2} \) resulting in the top semicircle from \(( -2, 0 )\) up through \(( 0, 6 )\) to \(( 2, 0 )\).
06
Combine the graphs
All these transformations should be drawn on the same coordinate plane to showcase the transformations due to different \( c \) values. This results in three semicircles corresponding to \( c = -2, 1, 3 \).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Semicircle Function
A semicircle function is a familiar quadratic function that forms a half-circle on the coordinate plane. In the case of the exercise, you're dealing with the function:
- \( y = \sqrt{4-x^2} \) represents the top half of a circle with a radius of 2.
- This is derived from the equation of a circle, \( x^2 + y^2 = 4 \), centered at the origin.
- The positive square root gives the upper semicircle.
Vertical Stretching
Vertical stretching is an important transformation that influences the height of a graph without changing it horizontally. This transformation is controlled by the value of \( c \) in the function \( f(x) = c \sqrt{4-x^2} \). Let's look at how this plays out:
- For \( c = 1 \), the graph maintains its original size, representing the basic semicircle.
- When \( c = 3 \), the graph stretches vertically by a factor of 3, making it three times taller, with the new highest point at \( (0, 6) \).
Reflection on X-Axis
A reflection on the x-axis flips a graph upside down. In mathematical terms, it is represented by a negative multiplier. Here, when \( c = -2 \), this reflection takes place:
- The original semicircle, \( y = \sqrt{4-x^2} \), turns into \( y = -2 \sqrt{4-x^2} \).
- This transformation flips the semicircle from above the x-axis to below it.
- Additionally, the semicircle is vertically stretched by a factor of 2.
- The lowest point reaches \( (0, -4) \).
Symmetry in Graphs
Symmetry in graphs is an essential concept that helps in understanding the balanced appearance of functions around a line or point. In our exercise, symmetry simplifies plotting:
- The base semicircle function, \( y = \sqrt{4-x^2} \), is symmetric about the y-axis.
- This means if you were to fold the graph along the y-axis, both halves would overlap perfectly.