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Ch. 2 - Functions and Graphs
Blitzer - College Algebra 8th Edition
Blitzer8th EditionCollege AlgebraISBN: 9780136970514Not the one you use?Change textbook
Chapter 3, Problem 95

Find all values of x satisfying the given conditions. f(x) = 2x − 5, g(x) = x² − 3x + 8, and (ƒ o g) (x) = 7.

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1
Understand that the composition (ƒ o g)(x) means ƒ(g(x)), which is the function ƒ applied to the output of g(x).
Write the composition explicitly: (ƒ o g)(x) = ƒ(g(x)) = 2(g(x)) - 5.
Substitute g(x) = x² - 3x + 8 into the expression: 2(x² - 3x + 8) - 5.
Set the expression equal to 7 as given: 2(x² - 3x + 8) - 5 = 7.
Solve the resulting quadratic equation by first expanding, then simplifying, and finally using factoring or the quadratic formula to find all values of x.

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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 (f o g)(x) = f(g(x)). It means you first evaluate g(x), then substitute that result into f. Understanding this process is essential to correctly set up and solve equations involving composed functions.
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Function Composition

Quadratic Functions

A quadratic function is a polynomial of degree two, typically written as ax² + bx + c. Recognizing the form and properties of quadratics helps in evaluating g(x) and simplifying expressions. Quadratic functions often require factoring or using the quadratic formula to find roots.
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Solving Equations

Solving equations involves finding all values of the variable that satisfy the given equality. In this problem, after composing the functions, you will get an equation to solve for x, which may be linear or quadratic. Techniques include isolating variables, factoring, or applying the quadratic formula.
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