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Even and Odd Functions, Symmetry, and Graph Shapes on the Coordinate Plane

Even and odd functions play an important role in understanding the symmetry and behavior of graphs. An even function is symmetric with respect to the y‑axis, while an odd function is symmetric with respect to the origin. Recognizing these properties helps us sketch graphs more quickly and analyze their behavior. This article explains the definitions of even and odd functions, how to identify them, types of symmetry, and how these properties affect the shape of graphs.

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~3 min read • Updated Feb 10, 2026

1. What Are Even Functions?


A function is called even if for every value of x we have:


f(-x) = f(x)

This relationship shows that the function is symmetric with respect to the y-axis.


Example of an Even Function:

f(x) = x^2

Since (-x)^2 = x^2, this function is even.


2. What Are Odd Functions?


A function is called odd if for every value of x we have:


f(-x) = -f(x)

This indicates symmetry with respect to the origin.


Example of an Odd Function:

f(x) = x^3

Since (-x)^3 = -x^3, this function is odd.


3. How to Determine Whether a Function Is Even or Odd


  • Substitute -x for x
  • If f(-x) = f(x) → the function is even
  • If f(-x) = -f(x) → the function is odd
  • If neither condition holds → the function is neither even nor odd

Example:

f(x) = x^2 + 1
f(-x) = (-x)^2 + 1 = x^2 + 1

So the function is even.


4. Symmetry in Function Graphs


Symmetry is an important feature that helps simplify graph sketching.


Types of Symmetry:

  • Symmetry about the y-axis: characteristic of even functions
  • Symmetry about the origin: characteristic of odd functions
  • Symmetry about the x-axis: usually not valid for functions (it violates the definition of a function)

5. Graph Shape of Even Functions


The graph of an even function is always symmetric with respect to the y-axis. If a point (a, b) lies on the graph, then (-a, b) also lies on the graph.


Example:

f(x) = x^2

The graph is a parabola symmetric about the y-axis.


6. Graph Shape of Odd Functions


The graph of an odd function is symmetric with respect to the origin. If a point (a, b) lies on the graph, then (-a, -b) also lies on the graph.


Example:

f(x) = x^3

The graph is an S-shaped curve symmetric about the origin.


7. Functions That Are Neither Even nor Odd


Many functions are neither even nor odd and have no specific symmetry.


Example:

f(x) = x^2 + x

Because:

f(-x) = x^2 - x

It is neither equal to f(x) nor -f(x).


8. Applications of Even and Odd Functions


  • Simplifying integrals
  • Faster graph analysis
  • Understanding behavior in positive and negative intervals
  • Applications in physics, signal processing, and wave analysis

9. Conclusion


Even functions are symmetric about the y-axis, while odd functions are symmetric about the origin. Recognizing these properties helps us sketch graphs more efficiently and analyze their behavior. Many functions are neither even nor odd and show no particular symmetry.


Written & researched by Dr. Shahin Siami

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