/*! This file is auto-generated */ .wp-block-button__link{color:#fff;background-color:#32373c;border-radius:9999px;box-shadow:none;text-decoration:none;padding:calc(.667em + 2px) calc(1.333em + 2px);font-size:1.125em}.wp-block-file__button{background:#32373c;color:#fff;text-decoration:none} Problem 69 Solving an Equation for an Unkno... [FREE SOLUTION] | 91Ó°ÊÓ

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Solving an Equation for an Unknown Function Suppose that $$\begin{array}{l}g(x)=2 x+1 \\\h(x)=4 x^{2}+4 x+7\end{array}$$ Find a function \(f\) such that \(f \circ g=h .\) (Think about what operations you would have to perform on the formula for \(g\) to end up with the formula for \(h .\) ) Now suppose that $$\begin{array}{l}f(x)=3 x+5 \\\h(x)=3 x^{2}+3 x+2\end{array}$$ Use the same sort of reasoning to find a function \(g\) such that \(f \circ g=h\)

Short Answer

Expert verified
First, \( f(x) = x^2 + 6 \). Second, \( g(x) = x^2 + x - 1 \).

Step by step solution

01

Understand the Function Composition

Given that \( f \circ g = h \), this implies \( f(g(x)) = h(x) \). Our task is to find the function \( f \) such that for the first pair \( g(x) = 2x + 1 \) and \( h(x) = 4x^2 + 4x + 7 \), and a function \( g \) such that for the second pair \( f(x) = 3x + 5 \) and \( h(x) = 3x^2 + 3x + 2 \).
02

Find f for the First Pair

We are given \( g(x) = 2x + 1 \). We want to find \( f \) such that \( f(g(x)) = 4x^2 + 4x + 7 \). Substitute \( g(x) \) into \( f \) which gives us \( f(2x + 1) \). Since \( f \circ g = h \), we have \( f(2x + 1) = 4x^2 + 4x + 7 \). To match this, let \( f(u) = au^2 + bu + c \), substitute \( u = 2x + 1 \), and match coefficients.
03

Equate and Solve Coefficients for f for First Pair

Substituting \( u = 2x + 1 \) into \( f(u) = au^2 + bu + c \) gives:\[ f(2x + 1) = a(2x+1)^2 + b(2x+1) + c = 4x^2 + 4x + 7 \].Expand \( (2x + 1)^2 = 4x^2 + 4x + 1 \), thus:\[ a(4x^2 + 4x + 1) + b(2x + 1) + c = 4x^2 + 4x + 7 \].Combine like terms to get:\[ (4a)x^2 + (4a + 2b)x + (a + b + c) = 4x^2 + 4x + 7 \].Equate coefficients: \( 4a = 4 \), \( 4a + 2b = 4 \), \( a + b + c = 7 \). Solve to find \( a = 1 \), \( b = 0 \), \( c = 6 \). Thus, \( f(u) = u^2 + 6 \).
04

Procedure for Finding g in the Second Pair

Given \( f(x) = 3x + 5 \) and \( h(x) = 3x^2 + 3x + 2 \), we need \( g \) such that \( f(g(x)) = 3x^2 + 3x + 2 \). Write \( g(x) \) in a form that when substituted into \( 3x + 5 \) will yield \( h(x) \). Let \( g(x) = ax^2 + bx + c \), then \( f(g(x)) = 3(ax^2 + bx + c) + 5 = 3x^2 + 3x + 2 \).
05

Determine g by Matching Terms for Second Pair

Substitute \( g(x) = ax^2 + bx + c \) into \( f \):\[ 3(ax^2 + bx + c) + 5 = 3x^2 + 3x + 2 \].This gives:\[ 3ax^2 + 3bx + 3c + 5 = 3x^2 + 3x + 2 \].Equate coefficients: \( 3a = 3 \), \( 3b = 3 \), \( 3c + 5 = 2 \). Solve to find \( a = 1 \), \( b = 1 \), \( c = -1 \). Therefore, \( g(x) = x^2 + x - 1 \).

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Polynomial Functions
Polynomial functions represent mathematical expressions involving terms made up of variables with non-negative integer exponents and constant coefficients. They come in various degrees, such as linear, quadratic, cubic, and so on, based on the highest power of the variable. In the given exercise, the functions we deal with are linear and quadratic.

For example, the function \( g(x) = 2x + 1 \) is linear because it has a degree of 1, and its graph forms a straight line. In contrast, \( h(x) = 4x^2 + 4x + 7 \) is a quadratic polynomial because it has a degree of 2, making its graph a parabola. Understanding the form and degree of these polynomial functions is essential because they inform us about how the function values behave as \( x \) changes.

Polynomial functions are at the heart of many algebraic operations and are critical when it comes to composing functions, solving equations, and matching coefficients, as practiced in the exercise. Composing a linear function into a quadratic one involves careful manipulation and understanding of polynomial structures.
Equation Solving
Equation solving involves finding the unknown values in a mathematical equation that makes the equation true. In this exercise, solving for functions involves deducing unknown functions \( f(x) \) or \( g(x) \) such that their composition with another given function results in a provided polynomial.

The process of function composition, \( f(g(x)) = h(x) \), requires solving this functional equation by substitution and equating terms from the resulting polynomial expressions. This involves ensuring that when substituting the expression for one function into another, the output matches the target polynomial function completely. Solution steps involve substituting known variable expressions, expanding polynomials, and equating corresponding coefficients to find the unknown parameters.

Typically, when solving these equations, you rely on algebraic manipulation and careful analysis of the terms following substitution within the context of polynomials. This skill is foundational for higher levels of mathematics, enabling problem-solving in diverse scenarios from algebra to calculus.
Coefficient Matching
Coefficient matching is a critical step in solving equations involving polynomials. It involves aligning the coefficients of corresponding terms of two polynomial expressions to find unknown values. In this exercise, it was used to deduce unknown functions in a composition.

For example, to find the function \( f(x) \) such that \( f(g(x)) = h(x) \), you substitute \( g(x) \) into \( f \)'s assumed polynomial form, resulting in an expression in terms of \( x \). After expanding and simplifying, you compare coefficients of \( x^2, x, \) and the constant terms between this expression and the target \( h(x) \). By equating these coefficients, you form a system of equations that allows solving for the unknown coefficients in \( f(x) \).

In the practical sense, coefficient matching provides a systematic way to ensure that one polynomial perfectly transforms into another through function composition. It's a powerful algebraic tool providing clarity and precision in polynomial transformations and function manipulations.

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Most popular questions from this chapter

At the beginning of this section we discussed three examples of everyday, ordinary functions: Height is a function of age, temperature is a function of date, and postage cost is a function of weight. Give three other examples of functions from everyday life.

If \(f(x)=m x+b\) is a linear function, then the average rate of change of \(f\) between any two real numbers \(x_{1}\) and \(x_{2}\) is $$\text { average rate of change }=\frac{f\left(x_{2}\right)-f\left(x_{1}\right)}{x_{2}-x_{1}}$$ Calculate this average rate of change to show that it is the same as the slope \(m\)

The population \(P\) (in thousands) of San Jose, California, from 1988 to 2000 is shown in the table. (Midycar estimates are given.) Draw a rough graph of \(P\) as a function of time \(t\) $$\begin{array}{|c|c|c|c|c|c|c|c|} \hline t & 1988 & 1990 & 1992 & 1994 & 1996 & 1998 & 2000 \\ \hline P & 733 & 782 & 800 & 817 & 838 & 861 & 895 \\ \hline \end{array}$$

As blood moves through a vein or an artery, its velocity \(v\) is greatest along the central axis and decreases as the distance \(r\) from the central axis increases (see the figure). The formula that gives \(v\) as a function of \(r\) is called the law of laminar flow. For an artery with radius \(0.5 \mathrm{cm},\) the relationship between \(v\) (in \(\mathrm{cm} / \mathrm{s}\) ) and \(r\) (in \(\mathrm{cm}\) ) is given by the function $$v(r)=18,500\left(0.25-r^{2}\right) \quad 0 \leq r \leq 0.5$$ (a) Find \(v(0.1)\) and \(v(0.4)\) (b) What do your answers to part (a) tell you about the flow of blood in this artery? (c) Make a table of values of \(v(r)\) for \(r=0,0.1,0.2,0.3\) \(0.4,0.5\) (image cannot copy)

Because of the curvature of the earth, the maximum distance \(D\) that you can see from the top of a tall building or from an airplane at height \(h\) is given by the function $$D(h)=\sqrt{2 r h+h^{2}}$$ where \(r=3960 \mathrm{mi}\) is the radius of the earth and \(D\) and \(h\) are measured in miles. (a) Find \(D(0.1)\) and \(D(0.2)\) (b) How far can you see from the observation deck of Toronto's CN Tower, \(1135 \mathrm{ft}\) above the ground? (c) Commercial aircraft fly at an altitude of about \(7 \mathrm{mi}\). How far can the pilot see?

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