How to Find Real Zeros of a Function – A Simple Guide to Roots

How to Find Real Zeros of a Function A Simple Guide to Roots

To find the real zeros of a function, I usually start by setting the function equal to zero and solving for the variable, typically x.

The real zeros, also simply called the roots, are the x-values where the function’s graph intersects the x-axis. For a given function ( f(x) ), this translates to finding the solutions to the equation ( f(x) = 0 ).

These real zeros are critical, as they reveal important characteristics of the behavior and the graph of the function.

In dealing with polynomials, the zeros of a function can often be found by factoring the polynomial into its simplest components, provided all the factors are real numbers.

For example, if I have a quadratic function like $f(x) = x^2 + 5x + 6 $, I can factor it into ( (x + 2)(x + 3) ), leading to the real zeros ( x = -2 ) and ( x = -3 ). Easier said than done sometimes, but patience and practice make the process smoother.

Stay tuned to learn more about methods for finding those elusive zeros, and why understanding them can be so useful for analyzing the behavior of functions.

Steps for Finding Real Zeros of Functions

When I’m tasked with finding the real zeros of a function, I follow a systematic process. Real zeros are the points where the graph of the function crosses the x-axis, and they correspond to the roots of the function.

Illustration of Steps for Finding Real Zeros of Functions

They can be rational or irrational numbers.

  1. Identify the type of function: First, I determine whether I’m dealing with a polynomial, quadratic, rational, or cubic function. Each type has specific methods for finding zeros.

  2. Analyzing the function’s degree: For polynomial functions, the degree hints at the maximum number of real zeros. A quadratic, for instance with a degree of 2, could have up to two real zeros.

  3. Use Graphical Representations: Plotting the function on a graph provides a visual aid. The points where the graph intersects the x-axis are the real zeros of the function.

  4. Factoring: If the function is factorable, I express it as a product of simpler polynomials. The values of the variable that make each factor zero are the real zeros.

  5. Quadratic formula: For quadratic functions, the quadratic formula $\left(\frac{-b\pm\sqrt{b^2-4ac}}{2a}\right)$ pinpoints the real zeros, when they exist.

  6. Rational Root Theorem: This is useful for polynomials with integer coefficients. If $f(x)=a_nx^n+\ldots+a_1x+a_0$, any rational zero $\frac{p}{q}$ must have $p$ as a factor of $a_0$ and $q$ as a factor of $a_n$.

  7. Apply Synthetic Division: Synthetic division is a streamlined method to test possible zeros provided by the Rational Root Theorem.

  8. Check for Irrational Zeros: Using the conjugate root theorem, if the coefficients are rational and there is an irrational zero, its conjugate will also be a zero.

  9. Input & Output Analysis: Considering the domain and range might offer clues. For example, if I know the output must be positive, zeros will only occur when the input leads to an output of zero.

By working through these steps, I usually capture all the real zeros of a function, revealing its crucial intersections with the x-axis.

Example Functions Solved for Real Zeros

When I approach a polynomial function, my goal is to find its roots or the real zeros. These are the values of ( x ) where the graph of a function crosses or touches the x-axis. Let’s consider a couple of examples:

Example 1: Quadratic Function
Given function: $ f(x) = x^2 – 5x + 6$
To find the real zeros, I can factor this quadratic function: ( (x – 2)(x – 3) = 0 ). Thus, the real zeros are ( x = 2 ) and ( x = 3 ).

Example 2: Cubic Function
Given function: $f(x) = x^3 – 6x^2 + 11x – 6$
The Rational Zero Theorem can help me here. If $\frac{p}{q}$ is a zero, then ( p ) is a factor of -6, and ( q ) is a factor of 1. Checking these possible zeros through synthetic division or the Factor Theorem, I find ( x = 1 ), ( x = 2 ), and ( x = 3 ) are the real zeros.

The Fundamental Theorem of Algebra tells us a polynomial of degree ( n ) will have exactly ( n ) complex zeros (which include real zeros), counting multiplicities. I can confirm the number of zeros using this theorem.

To represent this process systematically, I create a quick reference table for a quadratic function:

1Factoring$ (x – r_1)(x – r_2) = 0 $
2Find Zeros$x = r_1, x = r_2 $
3VerifyPlot on graph

In the examples, factoring was possible directly, but sometimes I may need to use the quadratic formula if the polynomial is a quadratic and cannot be factored easily. For higher-degree polynomials, techniques like synthetic division may be necessary.

Remember, the x-intercepts are another term for the real zeros of a function. Identifying roots visually through a graph of a function can also be a useful check.


In our journey to decipher the real zeros of a function, I’ve outlined several methods to support this mathematical endeavor.

From the graphical approach observing where a curve intersects the x-axis at points where $f(x) = 0$, to employing the Rational Zero Theorem, my goal was to clarify the process in a way that’s approachable and practical.

By tapping into theorems like the Intermediate Value Theorem, I’ve demonstrated how to confirm the existence of zeros within an interval. The use of Descartes’ Rule of Signs provided insight into the number of positive and negative zeros a polynomial might possess.

For polynomials in particular, the Linear Factorization Theorem was crucial in establishing the relationship between zeros and factors of the polynomial, converting a daunting task into a more manageable one. Each zero points to a factor, and recognizing this connection can simplify how we perceive polynomial functions.

Remember that finding the zeros of a function isn’t just a mechanical process—it’s a significant step in understanding the behavior of mathematical models in contexts ranging from physics to finance.

I hope these strategies not only serve as tools but also build a foundation for deeper insight into the fabric of algebra and its applications.