Skip to main content
Ch. 2 - Graphs and Functions
Lial - College Algebra 13th Edition
Lial13th EditionCollege AlgebraISBN: 9780136881063Not the one you use?Change textbook
Chapter 3, Problem 75b

Given functions f and g, find (b)(gƒ)(x)(g∘ƒ)(x) and its domain. See Examples 6 and 7.
ƒ(x)=x,g(x)=x+3ƒ(x)=√x, g(x)=x+3

Verified step by step guidance
1
Identify the given functions: \( f(x) = \sqrt{x} \) and \( g(x) = x + 3 \).
Recall that the composition \( (g \circ f)(x) \) means \( g(f(x)) \), which is applying \( f \) first, then \( g \) to the result.
Substitute \( f(x) \) into \( g \): \( (g \circ f)(x) = g(\sqrt{x}) = \sqrt{x} + 3 \).
Determine the domain of \( (g \circ f)(x) \) by considering the domain of \( f(x) \) first, since \( f \) is applied first. Since \( f(x) = \sqrt{x} \), the domain is \( x \geq 0 \) because the square root requires non-negative inputs.
Since \( g(x) = x + 3 \) is defined for all real numbers, the domain of \( (g \circ f)(x) \) is the same as the domain of \( f(x) \), which is \( x \geq 0 \).

Verified video answer for a similar problem:

This video solution was recommended by our tutors as helpful for the problem above.
Video duration:
2m
Was this helpful?

Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Function Composition

Function composition involves applying one function to the result of another, denoted as (g∘f)(x) = g(f(x)). It means you first evaluate f at x, then use that output as the input for g. Understanding this process is essential to correctly find (g∘f)(x).
Recommended video:
4:56
Function Composition

Domain of a Function

The domain of a function is the set of all input values for which the function is defined. When composing functions, the domain of (g∘f) depends on the domain of f and the domain restrictions of g applied to f(x). Identifying these restrictions ensures the composition is valid.
Recommended video:
3:51
Domain Restrictions of Composed Functions

Square Root Function Domain

The square root function ƒ(x) = √x is defined only for x ≥ 0 because the square root of a negative number is not a real number. This domain restriction affects the composition since f(x) must produce values within g's domain, and x must satisfy x ≥ 0.
Recommended video:
02:20
Imaginary Roots with the Square Root Property