Parent Function in Math: Definition & Examples

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  • 0:00 Parent Functions Defined
  • 2:38 Example: Exponential Functions
  • 4:14 More Examples
  • 6:20 Lesson Summary
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Lesson Transcript
Instructor: Laura Pennington

Laura has taught collegiate mathematics and holds a master's degree in pure mathematics.

This lesson will familiarize us with parent functions. We will look at many examples to learn the definitions of both families of functions and parent functions. We will also look at identifying a parent function in a family of functions.

Parent Functions

When you hear the term parent function, you may be inclined to think of two functions who love each other very much creating a new function.

Parent Function
parent function cartoon

Well, that's not exactly right; however, there are some similarities that we can observe between our own parents and parent functions. In mathematics, we have certain groups of functions that are called families of functions. Just like our own families have parents, families of functions also have a parent function.

The similarities don't end there! In the same way that we share similar characteristics, genes, and behaviors with our own family, families of functions share similar algebraic properties, have similar graphs, and tend to behave alike. An example of a family of functions are the quadratic functions. All quadratic functions have a highest exponent of 2, their graphs are all parabolas so they have the same shape, and they all share certain characteristics.

Quadratic Family of Functions
parabola family of functions

As mentioned above, each family of functions has a parent function. A parent function is the simplest function that still satisfies the definition of a certain type of function. For example, when we think of the linear functions which make up a family of functions, the parent function would be y = x. This is the simplest linear function.

Furthermore, all of the functions within a family of functions can be derived from the parent function by taking the parent function's graph through various transformations. These transformations include horizontal shifts, stretching or compressing vertically or horizontally, reflecting over the x or y axes, and vertical shifts. For example, in the above graph, we see that the graph of y = 2x^2 + 4x is the graph of the parent function y = x^2 shifted one unit to the left, stretched vertically, and shifted down two units. These transformations don't change the general shape of the graph, so all of the functions in a family have the same shape and look similar to the parent function.

Algebraically, these transformations correspond to adding or subtracting terms to the parent function and to multiplying by a constant. For example, the function y = 2x^2 + 4x can be derived by taking the parent function y = x^2, multiplying it by the constant 2, and then adding the term 4x to it.

Example: Exponential Functions

To illustrate this, let's consider exponential functions. Exponential functions are functions of the form y = ab^x, where a and b are both positive (greater than zero), and b is not equal to one. Basically, exponential functions are functions with the variable in the exponent. The number b is the base of the exponential function. Let's consider the family of functions that are exponential functions with base 2. Some functions that are in this family of functions are shown below.

exponential functions

Notice that the simplest exponential function in the above family is y = 2^x. This is the parent function of the family of functions. In general, the simplest exponential function is y = b^x where b > 1. This is the parent function of exponential functions with base b. The graph below displays the graphs of all of the functions listed above. Observe that they all have the same shape as the parent function and that they can all be derived by performing the transformations previously mentioned to the parent function.

Exponential Family of Functions With Base 2
graph of exponential functions with base 2

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