How to Know if a Function is Even or Odd – Quick Identification Tips

How to Know if a Function is Even or Odd Quick Identification Tips

To determine if a function is even or odd, I first perform a simple substitution: for any function ( f(x) ), replace ( x ) with ( -x ). If the resulting function ( f(-x) ) is identical to the original ( f(x) ), the function is even, reflecting symmetry about the y-axis.

Conversely, if ( f(-x) ) equates to ( -f(x) ), the function demonstrates odd symmetry, pivoting about the origin. Applying algebraic manipulation to this substitution helps me establish the function’s parity without requiring a graph.

When dealing with more complex functions or when the symmetry isn’t immediately apparent, I rely on this algebraic approach to scrutinize the behavior of the function under the transformation $x \to -x $.

It serves as an insightful tool for understanding the foundational concepts of symmetry in algebraic functions. Stay tuned to discover what fascinating characteristics these even and odd functions have to offer.

Understanding Even and Odd Functions

When I look at even and odd functions, I’m focusing on their symmetrical properties, particularly in relation to the y-axis, the x-axis, and the origin.

Even functions exhibit symmetry about the y-axis. If I were to fold the graph along the y-axis, both sides would match up perfectly, like a mirror reflection.

On a more technical level, a function ( f(x) ) is even if, for every ( x ) in the domain, the following condition holds true:

$$ f(x) = f(-x) $$

For example, $ f(x) = x^2$ is an even function because $ f(-x) = (-x)^2 = x^2$, which is equal to ( f(x) ).

( x )( f(x) )( f(-x) )

Odd functions, in contrast, have origin symmetry. This means that if I rotate the graph 180 degrees around the origin, it would look the same. Algebraically, a function ( f(x) ) is odd if the following is true for all ( x ):

$$ f(-x) = -f(x) $$

An example of an odd function is $f(x) = x^3 ), since ( f(-x) = (-x)^3 = -x^3 = -f(x)$.

( x )( f(x) )( f(-x) )

To determine whether a function is even, odd, or neither, I graph the function or use algebraic manipulation. If the function doesn’t satisfy either of the criteria above, then it is neither even nor odd.

It’s important to remember that some functions do not exhibit any symmetrical properties and therefore fall into this third category.

Steps Involved in Finding Odd or Even Functions

When I approach the task of determining whether a function is even, odd, or neither, I begin by reviewing its algebraic form. Here is a structured method I use:

  1. Identify the Function: I start with the given function, for example, $f(x) = ax^n$ where a is a constant and n is an exponent. This function can be a polynomial or any other algebraic expression.

  2. Test for Evenness: To test for evenness, I replace $x$ with $-x$ and observe if the function remains unchanged. In other words, I check if $f(-x) = f(x)$. An even function exhibits symmetry about the y-axis. Here’s a simple representation:

Original FunctionTransformed FunctionEven?
$f(x)$$f(-x)$Is $f(-x) = f(x)$?
  1. Test for Oddness: Alternatively, for oddness, I replace $x$ with $-x$ and determine if the result is the negative of the original function, which means $f(-x) = -f(x)$. Odd functions display symmetry about the origin.
Original FunctionTransformed FunctionOdd?
$f(x)$$f(-x)$Is $f(-x) = -f(x)$?
  1. Evaluate Exponents: In a polynomial, the powers of $x$ often give me a clue. If all exponents are even, the function is a candidate for being even. Conversely, if all exponents are odd, the function may be odd. Mixed exponents require a full evaluation.

  2. Check Constant Terms: A function with a non-zero constant term cannot be odd since $f(x)$ and $f(-x)$ would differ by this constant.

  3. Simplify and Compare: After plugging in $-x$, I simplify the expression. The signs and terms resulting from this simplification tell me whether the function is even, odd, or neither, depending on whether they match the original function or its negative.

Following these steps, I confidently determine the nature of most algebraic functions according to their symmetry properties.

Applying the Vertical Line Test

When I want to determine whether a graph represents a function or not, I use a simple yet effective tool called the vertical line test. Here’s how it works:

  1. Visual Inspection: I first look at the graph of the curve to see its overall shape and symmetry. A curve might display characteristics that suggest it could be a function, but looks can be deceiving. That’s where the vertical line test comes in handy.

  2. Drawing Vertical Lines:

    • I draw or imagine a series of vertical lines that pass through the graph.
    • I make sure to cover the entire domain of the curve with these lines.
  3. Checking Intersections:

    • One Intersection: If each vertical line touches the graph at exactly one point, then I have a match. The curve represents a function because each input (or $x$-value) is associated with only one output (or $y$-value).
    • Multiple Intersections: If a vertical line intersects the graph at more than one point, then the symmetry is broken. The curve does not represent a function.

Here’s a quick reference table I keep in mind:

Vertical Line Test ResultImplication
One intersectionFunction (passes the test)
More than one intersectionNot a function (fails the test)

I remember that the vertical line test is a great tool to visually assess the function-ness of a graph, but it doesn’t tell me whether the function is even or odd.

For that, I’ll need to look at other properties like whether the function exhibits symmetry about the y-axis (even) or origin (odd). Using these tools together gives a clear mathematical picture of any curve I’m studying.

Operational Properties of Even and Odd Functions

When dealing with the addition and multiplication of functions, it’s useful to understand how the properties of even and odd functions behave. Even functions satisfy the condition $f(-x) = f(x)$, whereas odd functions satisfy $f(-x) = -f(x)$.

Sum and Difference Formulas:

  • The sum of two even functions is also even. For example, if $f(x)$ and $g(x)$ are even, then $f(x) + g(x)$ is even because $f(-x) + g(-x) = f(x) + g(x)$.
  • The difference between the two even functions remains even. Using the same functions, $f(x) – g(x)$ is even.
  • The sum or difference of two odd functions is odd. So if $h(x)$ and $k(x)$ are odd, $h(x) ± k(x)$ will yield another odd function.


  • The product of two even functions is even. For $f(x) * g(x)$, both producing $f(x)$ and $g(x)$ will result in an even function since the product of two positives or two negatives is positive.
  • Conversely, the product of two odd functions is even, because a negative times a negative gives a positive.

Special Cases in Trigonometry:

  • The Trigonometric functions display these properties as well.
  • The sine function, $\sin(x)$, is odd since $\sin(-x) = -\sin(x)$.
  • The cosine function, $\cos(x)$, is even as $\cos(-x) = \cos(x)$.
OperationEven and EvenEven and OddOdd and Odd

Lastly, the zero function, $f(x) = 0$, holds a unique position as it is the only function that is both even and odd.


In our exploration of even and odd functions, I’ve highlighted the simple algebraic tests that can determine a function’s symmetry.

Remember, an even function satisfies the condition ( f(x) = f(-x) ) for all values of ( x ), indicating symmetry about the y-axis. In contrast, an odd function meets ( f(-x) = -f(x) ), reflecting origin symmetry.

To solidify my understanding, I often practice by applying these tests to different functions. For instance, the function $f(x) = x^2$ is even because $f(-x) = (-x)^2 = x^2$, which is identical to ( f(x) ).

Alternatively, $f(x) = x^3$ is odd because $ f(-x) = (-x)^3 = -x^3 $, which is the negative of ( f(x) ). Functions that do not fulfill either condition are classified as neither even nor odd.

I encourage you to apply these checks to any function you come across—it’s a quick and effective way to deepen your mathematical comprehension.

Having this skill in your toolkit is invaluable, aiding in the analysis of functions and their graphs. Whether you’re solving calculus problems or scrutinizing mathematical models, identifying the nature of functions paves the way for enhanced problem-solving strategies.