Piecewise-Defined Functions | College Algebra - Lumen Learning

Home » How To Write Piecewise Functions » Piecewise-Defined Functions | College Algebra - Lumen Learning

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Learning Outcomes

  • Write piecewise defined functions.
  • Graph piecewise-defined functions.

Sometimes, we come across a function that requires more than one formula in order to obtain the given output. For example, in the toolkit functions, we introduced the absolute value function [latex]f\left(x\right)=|x|[/latex]. With a domain of all real numbers and a range of values greater than or equal to 0, absolute value can be defined as the magnitude, or modulus, of a real number value regardless of sign. It is the distance from 0 on the number line. All of these definitions require the output to be greater than or equal to 0.

If we input 0, or a positive value, the output is the same as the input.

[latex]f\left(x\right)=x\text{ if }x\ge 0[/latex]

If we input a negative value, the output is the opposite of the input.

[latex]f\left(x\right)=-x\text{ if }x $10,000[/latex] .

A General Note: Piecewise Functions

A piecewise function is a function in which more than one formula is used to define the output. Each formula has its own domain, and the domain of the function is the union of all these smaller domains. We notate this idea like this:

[latex]f\left(x\right)=\begin{cases}\text{formula 1 if x is in domain 1}\\ \text{formula 2 if x is in domain 2}\\ \text{formula 3 if x is in domain 3}\end{cases}[/latex]

In piecewise notation, the absolute value function is

[latex]|x|=\begin{cases}\begin{align}x&\text{ if }x\ge 0\\ -x&\text{ if }x

Tag » How To Write Piecewise Functions