Chapter 1: Problem 81
Test the equation for symmetry. $$y=x^{3}+10 x$$
Short Answer
Expert verified
The equation is symmetric about the origin only.
Step by step solution
01
Test for Symmetry about the x-axis
To test for symmetry about the x-axis, replace \( y \) with \( -y \) in the equation. The equation becomes: \(-y = x^3 + 10x\). Solve for \( y \): \( y = -x^3 - 10x\). The equation \( -y = x^3 + 10x \) does not match the original \( y = x^3 + 10x \), so it is not symmetric about the x-axis.
02
Test for Symmetry about the y-axis
To test for symmetry about the y-axis, replace \( x \) with \( -x \) in the equation. The equation becomes: \( y = (-x)^3 + 10(-x) \), which simplifies to: \( y = -x^3 - 10x \). The resulting equation \( y = -x^3 - 10x \) is not the same as the original \( y = x^3 + 10x \), indicating it is not symmetric about the y-axis.
03
Test for Symmetry about the Origin
To test for symmetry about the origin, replace \( x \) with \( -x \) and \( y \) with \( -y \). The equation becomes: \(-y = (-x)^3 + 10(-x)\), which simplifies to: \(-y = -x^3 - 10x\). Solving for \( y \), we get: \( y = x^3 + 10x \). This matches the original equation, indicating it is symmetric about the origin.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Symmetry About the X-axis
Symmetry about the x-axis occurs when a graph looks the same on the upper and lower halves of the x-axis. To test for this type of symmetry, we replace every instance of the variable \( y \) in the equation with \( -y \). For example, if the equation changes from \( y = x^3 + 10x \) to \( -y = x^3 + 10x \), and further manipulation yields \( y = -x^3 - 10x \), then:
- The modified equation does not match the original equation.
- This indicates that the graph is not symmetric about the x-axis.
Symmetry About the Y-axis
Symmetry about the y-axis means that if you fold the graph along the y-axis, both sides match perfectly. To test this, substitute \( x \) with \( -x \) in the equation. For example, transforming \( y = x^3 + 10x \) to \( y = (-x)^3 + 10(-x) \) simplifies to \( y = -x^3 - 10x \).
- The resulting equation is \( y = -x^3 - 10x \), which does not match the original equation.
- This confirms that the graph is not symmetric about the y-axis.
Symmetry About the Origin
Symmetry about the origin implies a kind of rotational symmetry, where if you rotate the graph 180 degrees, it looks the same. To test for this symmetry, replace both \( x \) with \( -x \) and \( y \) with \( -y \).For instance, starting with \( y = x^3 + 10x \), replace to get \(-y = (-x)^3 + 10(-x)\) which simplifies back to \( y = x^3 + 10x \).
- The equation returns to its original form after replacing variables.
- This indicates the graph is symmetric about the origin.