What is Function Notation: Definition & Examples

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  • 0:01 What Is Notation?
  • 3:03 Writing with Function Notation
  • 5:05 Evaluating Functions
  • 6:57 Function Composition
  • 8:47 Lesson Summary
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Lesson Transcript
Instructor: David Liano
After completing this lesson, you will be able to recognize function notation. You will also be able to evaluate functions correctly using function notation.

What Is Notation?

Notation is a system of signs or symbols that represent words, numbers, phrases, etc. Notation is often designed for a specific purpose and is very helpful in communicating words, numbers, and other things in an efficient manner.

A good example of notation is musical notation. This type of notation system contains many symbols and various types of graphics, and it allows a composer to inform others how he wants his or her music to sound and be performed. Musical notation can be intimidating when one is first exposed to it; however, once learned, it allows a musician or aspiring musician to write music and to learn the music of others.

Function notation is a system of symbols used in mathematics, but it is arguably much easier to learn than musical notation. Function notation is an efficient and effective way to display functions of all types in mathematics. Let's start with a linear function. Many students are familiar with seeing linear functions written as y = 3x + 7.

This is a linear function in slope-intercept form. It is written with the standard y-variable in terms of the x-variable, which is the input variable, or independent variable. This is generally how students first learn how to write functions in mathematics. It is a good way of exposing students to functions; however, y = 3x + 7 is not written in function notation. Let's call this function f. We can then rewrite it with function notation: f(x) = 3x + 7.

All we did is replace y with f(x), so y = f(x). We can read this symbol as the value of f at x or as f of x. This way of writing a function gives us more flexibility and a better way of communicating how a function needs to be evaluated.

Let's evaluate this function when x = 5. With function notation, the instructions are very simple: find f(5). This tells us to evaluate function f when x = 5. In other words, replace x with 5 and solve: f(5) = 3(5) + 7 = 15 + 7 = 22.

Let's try another example. Find f(7) for f(x) = x^2 - 10x: f(7) = 7^2 - 10(7) = 49 - 70 = -21.

Writing With Function Notation

Even though it is common to use the letter f when writing function notation, any letter can be used in either upper or lower case. We can also change the letter for the input variable, but it tends to stay in lower case. This flexibility provides valuable maneuverability in writing functions.

Let's say we wanted to write a function for the area of a square. We could call the function A for area and use the letter s for side length of the square. This would give us the function notation of A(s) = s^2. This notation tells us that the area of a square with side length of s is s^2.

Using this definition of function A, let's evaluate the following: A(6). A(6) = 6^2 = 36 square units.

We can use function notation for functions that have multiple input variables. The formula for the volume of a rectangular prism is V = lwh. The volume of a rectangular prism is a function of the prism's length (l), width (w), and height (h).

We can write this formula using function notation: V(l, w, h) = lwh. Let's evaluate V(3, 7, 2). The function notation tells us that the rectangular prism has a length of 3 units, a width of 7 units, and a height of 2 units: V(3, 7, 2) = (3)(7)(2) = 42 cube units.

As long as you are told how a function and its input variables are defined, function notation allows efficient communication of a problem.

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