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Home / Mathematics / Understanding Cubic Functions: Definition, Properties, & Graphing with Solved Examples

Understanding Cubic Functions: Definition, Properties, & Graphing with Solved Examples

Last Updated on Mar 19, 2025
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What is Cubic Function?

A cubic function is a polynomial function of degree three, which means that the highest power of the variable is . The general form of a cubic function is , where , , , and are constants. The coefficient a determines the shape of the curve and whether the function has a maximum or minimum value.

Cubic functions have been studied for centuries, with early Greek mathematicians attempting to solve cubic equations using geometric methods. However, it was not until the 16th century that Italian mathematicians like Niccolò Tartaglia and Gerolamo Cardano developed algebraic methods for solving cubic equations.

Cubic Function Examples

The parent cube function, , always has a minimum of one real root due to the odd degree polynomial involved. For instance, has only one real root, . Therefore, the cubic function has one real and two complex roots. Some examples of cubic functions are provided below.

Domain and Range of Cubic Function

The domain and range of a cubic function depend on the coefficients of the function. In general, the domain of a cubic function is all real numbers . However, the range of a cubic function can vary based on the coefficients.

For the basic cubic function , the domain and range are both all real numbers.

  • If the coefficient of is positive, the cubic function has a minimum point, and its range is [-coordinate of the minimum point, ). The domain remains all real numbers.
  • If the coefficient of is negative, the cubic function has a maximum point, and its range is (, -coordinate of the maximum point]. The domain remains all real numbers.

Overall, the domain and range of a cubic function can vary, and it is essential to determine the coefficients of the function to determine its domain and range accurately.

Properties of Cubic Functions

Cubic functions, also known as third-degree polynomial functions, have unique characteristics that distinguish them from other polynomial functions. Below are some of the significant properties of cubic functions:

  • Degree: Cubic functions are third-degree polynomials, which means the highest exponent in the function is .
  • Roots: Cubic functions have a minimum of one real root, and it can have up to three roots, either real or complex. The roots can be found using various methods such as factoring, synthetic division, and the quadratic formula.
  • Turning points: Cubic functions have two turning points or points of inflection, where the concavity of the curve changes. The turning points occur where the second derivative of the function is zero.
  • Symmetry: A cubic function is neither even nor odd. However, it can exhibit some degree of symmetry, such as having a -axis symmetry if the function has no term ().
  • End Behavior: The end behavior of cubic functions is similar to that of quadratic functions. When approaches positive or negative infinity, the function's value also approaches positive or negative infinity, respectively.
  • Intercept with y-axis: The -intercept of a cubic function is always the constant term since .
  • Minimum or Maximum value: A cubic function has either a minimum or maximum value at the point where the turning point occurs.

Understanding these properties can help in graphing and analyzing cubic functions, making it an essential topic in algebra, calculus, and other related fields of mathematics.

Graphing Cubic Functions

Graphing cubic functions is a crucial aspect of studying them. Here are the steps to graph a cubic function:

Step 1:- Determine the intercepts: A cubic function intersects the -axis at least once, and it may or may not intersect the -axis. To find the -intercepts, set the function equal to zero and solve for . To find the -intercept, substitute in the function.

Step 2:- Find the end behavior: The end behavior of a cubic function is determined by the sign of its leading coefficient. If the leading coefficient is positive, then the function goes up on the right side and down on the left side. If the leading coefficient is negative, then the function goes down on the right side and up on the left side.

Step 3:- Locate the turning points: A cubic function has one or two turning points, depending on its shape. To find the turning points, take the derivative of the function and solve for the critical values. Then, plug these values back into the original function to find the -coordinate of the turning points.

Step 4:- Sketch the curve: Using the information obtained from the previous steps, sketch the curve of the cubic function. Make sure to label the intercepts, turning points, and end behavior.

Step 5:- Check your graph: To check your graph, you can use a graphing calculator or plot a few points on the curve and connect them.

Here is an example of graphing a cubic function: .

  • Find the -intercept(s): We already found that the -intercept of is .
  • Find the -intercept: We already found that the -intercept of is .
  • Find the critical point(s) by setting . . By quadratic formula, .
  • Find the corresponding -coordinate(s) of the critical points by substituting each of them in the given function. , . Therefore, the critical points are and .
  • Find the end behavior of the function. Since the leading coefficient of the function is which is , its end behavior is: as and as .
  • Plot all the points from Step 1, Step 2, and Step 4. Join them by a curve (also extend the curve on both sides) keeping the end behavior from Step 5 in mind.

Applications of Cubic Function

Cubic functions are widely used in many areas of mathematics and science due to their unique properties. Here are some applications of cubic functions:

  • Physics: Cubic functions are commonly used in physics to model the motion of objects under certain conditions, such as a ball thrown through the air.
  • Engineering: Engineers use cubic functions to model the behavior of materials, such as the deformation of a bridge or the stress on an airplane wing.
  • Economics: Cubic functions can be used to model supply and demand curves, which are important concepts in economics.
  • Computer Graphics: Cubic functions are used to create smooth curves and surfaces in computer graphics, such as in 3D animation and video game design.
  • Finance: Cubic functions can be used in finance to model financial data, such as stock prices or interest rates.
  • Cryptography: Cubic functions are used in some encryption algorithms for secure communication.

Cubic Function Solved Examples

1.Find the zeros of the cubic function .

Solution:

To find the zeros, we can use the rational root theorem to guess some possible rational roots. Since the leading coefficient is , the possible rational roots are , , , , , and . 

Testing each of these values, we find that is a root. 

Using synthetic division, we get . 

The quadratic factor can be solved using the quadratic formula to get , so the zeros are , , and .

2.Find the maximum value of the cubic function .

Solution:

To find the maximum value, we can take the derivative of the function and set it equal to zero to find the critical points. 

The derivative is , which has roots and . Checking the second derivative, we find that , so the critical point is a local maximum. 

Evaluating the function at , we get , so the maximum value is .

3.Find the inverse of the cubic function .

Solution:

To find the inverse, we switch the and variables to get , then solve for in terms of . 

Subtracting from both sides, we get , so . 

Therefore, the inverse function is .

Conclusion

Cubic functions might look a little tricky at first, but once you get the hang of their twists and turns, they’re actually super fun—and useful! Whether you're tackling SAT, ACT, GED, or AP Math problems, knowing how to graph, analyze, and apply cubic functions will give you a real edge. Plus, they're everywhere in real life—from physics to finance. Master them now, and you’re ahead of the game!

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