Chapter 3: Problem 72
71–72 ? Sketch the graph of each function. $$ f(x)=x^{3} \quad \text { (b) } g(x)=\left|x^{3}\right| $$
Short Answer
Expert verified
Graph \( f(x) = x^3 \) as a symmetric 'S' through the origin. Reflect negatives upwards for \( g(x) = |x^3| \).
Step by step solution
01
Understanding the function f(x)
The function \( f(x) = x^3 \) is a cubic function. It has no transformations such as shifts, stretches, or reflections.
02
Sketching the graph of f(x)
The graph of \( f(x) = x^3 \) passes through the origin \( (0,0) \), is symmetric with respect to the origin (odd function), and has a general 'S' shape that becomes steeper as \( x \) moves away from zero. Plot points for \( x = -2, -1, 0, 1, 2 \) to visualize the curve.
03
Understanding the function g(x)
The function \( g(x) = |x^3| \) is the absolute value of the cubic function. This means the graph of \( f(x) = x^3 \) is reflected over the x-axis for the part where \( x < 0 \).
04
Sketching the graph of g(x)
The graph of \( g(x) = |x^3| \) is similar to \( f(x) = x^3 \) for \( x \geq 0 \), but the portion where \( x < 0 \) is reflected upwards. Thus, for \( x < 0 \), plot points to mirror those of \( f(x) = -x^3 \).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Cubic Functions
Cubic functions are polynomial functions of degree three. The general form of a cubic function is given by: \[ f(x) = ax^3 + bx^2 + cx + d \] where \( a, b, c, \) and \( d \) are constants, and \( a eq 0 \). In the simplest case, as seen with \( f(x) = x^3 \), the function has no linear or constant term modifications. The graph of a cubic function has a characteristic 'S' shape. This is due to the fact that as \( x \) varies, the sign of the cubic term dominates the growth, leading to distinct curvatures as it moves through the origin.
- For large positive \( x \), \( x^3 \) increases rapidly, resulting in upward growth.
- For large negative \( x \), \( x^3 \) decreases rapidly, leading to downward growth.
Absolute Value
Understanding the absolute value involves grasping how it affects functions, both visually and algebraically. The absolute value of a function like \( g(x) = |x^3| \) takes each output value \( y = x^3 \) and applies the absolute value operation. This operation converts any negative result into a positive one. As a result, the negative portion of the graph of \( x^3 \) is reflected over the x-axis.
- For \( x \geq 0 \), the function remains unchanged \( g(x) = x^3 \).
- For \( x < 0 \), the function transforms, reflecting to \( g(x) = -x^3 \), ensuring all output values are positive or zero.
Odd Function
Odd functions have a distinctive symmetry property. A function \( f(x) \) is classified as odd if for every point \( (x, y) \) on the graph, there is a corresponding point \( (-x, -y) \). Symbolically, this is expressed as:\[ f(-x) = -f(x) \]For the cubic function \( f(x) = x^3 \), each term contributes to this odd symmetry. The function passes through the origin and has this reflectional balance about the origin itself, confirming its status as an odd function.
- Reflective Symmetry: Plotting the graph will reveal that it appears the same when rotated 180 degrees about the origin.
- Perfect Balance: The steepness and declining curves counterbalance on opposite sides of the origin, creating a natural symmetry.
Reflections
Reflections are transformations that "flip" the graph of a function over a line, typically the x-axis or y-axis. In terms of the current context, reflections occur due to absolute values applied to the cubic function, \( g(x) = |x^3| \).
- For the function \( g(x) \), reflection happens where \( x < 0 \). The graph of \( x^3 \) which would normally appear below the x-axis is lifted above the x-axis, mirroring the positive side.
- This results in all parts of the graph being within the first and second quadrants (since negative outputs are not possible).