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Let \(f(x)=\frac{1}{x}+x\) and \(g(x)=\frac{2 x}{x^{2}+1} .\) Evaluate the following expressions. (a) \(f(g(x))\) (b) \(g(f(x))\)

Short Answer

Expert verified
The results are \(f(g(x))=\frac{x^{2}+1}{2x}+\frac{2x}{x^{2}+1}\) and \(g(f(x)) = \frac{2}{x}+2x / \left(\frac{1}{x^{2}}+2+1+x^{2}\right)\).

Step by step solution

01

Evaluate \(f(g(x))\)

We will first find \(f(g(x))\), that means we plug \(g(x)\) into \(f(x)\). So the input for \(f(x)\), which is \(x\), is replaced by the function \(g(x) = \frac{2 x}{x^{2}+1}\). Therefore, \(f(g(x))\) becomes \(\frac{1}{g(x)}+g(x) = \frac{1}{\frac{2 x}{x^{2}+1}}+\frac{2 x}{x^{2}+1}\).
02

Simplify \(\frac{1}{g(x)}\)

The expression \(\frac{1}{g(x)}\) simplifies to the fraction \(\frac{x^{2}+1}{2x}\) by flipping the fraction. Thus, \(f(g(x))\) simplifies into \(\frac{x^{2}+1}{2x}+ \frac{2x}{x^{2}+1}\).
03

Evaluate \(g(f(x))\)

We find \(g(f(x))\), which means plug \(f(x)\) into \(g(x)\). So the input of \(g(x)\), which is \(x\), is replaced by the function \(f(x) = \frac{1}{x}+x\). The function \(g(f(x))\) then simplifies into \(\frac{2 (\frac{1}{x}+x)}{(\frac{1}{x}+x)^{2}+1}\).
04

Simplify \(g(f(x))\)

To simplify \(g(f(x))\), first distribute the \(2\) in the numerator to get \(\frac{2}{x}+2x\). Now, square the denominator as \((\frac{1}{x}+x)^{2} = \frac{1}{x^2}+2+x^2\). Add 1 to it to get the complete denominator as \(\frac{1}{x^2}+2+x^2+1\). Therefore, the simplified \(g(f(x))\) becomes \(\frac{2}{x}+2x / \left(\frac{1}{x^{2}}+2+1+x^{2}\right)\).

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Key Concepts

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

Rational Functions
Rational functions are a fundamental part of algebra involving ratios of polynomials. In our exercise, the functions \(f(x)\) and \(g(x)\) are rational functions. The function \(f(x) = \frac{1}{x} + x\) combines a simple rational term \(\frac{1}{x}\) with a linear term \(x\). Similarly, \(g(x) = \frac{2x}{x^2+1}\) is a purely rational function, with both the numerator and the denominator being polynomials.
Understanding rational functions is crucial because they appear frequently in various mathematical models and real-world applications, such as in physics and economics. Key characteristics of rational functions include:
  • They can have vertical asymptotes, holes, or horizontal asymptotes based on the degrees of the polynomials involved.
  • Their domain is the set of all real numbers except those values that make the denominator zero.
  • They often require simplification, which involves combining like terms and reducing fractions.
The exercise requires evaluating compositions of such functions, making it essential to grasp the behavior and properties of rational functions.
Simplifying Algebraic Expressions
Simplifying algebraic expressions is a vital skill in mathematics that involves reducing expressions to their simplest form. This process involves a range of algebraic manipulations such as distributing, combining like terms, and reducing fractions.
In the original solution, the expression \(f(g(x))\) simplify by finding the reciprocal of \(g(x)\) and adding \(g(x)\) itself, resulting in \(\frac{x^2+1}{2x} + \frac{2x}{x^2+1}\). Breaking each part into smaller pieces makes the whole expression easier to handle and understand.
When simplifying \(g(f(x))\), we noticed that distributing the numerator and squaring the denominator involved several steps:
  • Distributing \(2\) into the expression \(\frac{1}{x} + x\) to form \(\frac{2}{x} + 2x\).
  • Squaring the denominator accurately as \((\frac{1}{x} + x)^2 + 1\).
  • Re-visiting each component separately can ensure accuracy in simplifying complex expressions.
By understanding these simplification techniques, you can efficiently handle complex algebraic expressions that you will encounter in mathematics.
Mathematical Notation
Mathematical notation serves as the language of math, providing a universal way to express complex ideas succinctly. In the exercise, we used different notations to represent function composition and expression evaluations efficiently. Notation plays a significant role in understanding the operations involved during calculations, especially for functions.
Some key notational structures in this exercise include:
  • Representation of functions. For instance, \(f(x)\) and \(g(x)\) denote different functions applied to the variable \(x\).
  • Function Composition. The expression \(f(g(x))\) shows that function \(g(x)\) is substituted into \(f(x)\).
  • Use of division and fraction notations to indicate the division of polynomials clearly, such as \(\frac{1}{x}\).
Math notation simplifies complex operations, allowing us to communicate and solve problems more effectively. By practicing with these notations, students will improve their problem-solving skills and ability to tackle intricate mathematical challenges.

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Most popular questions from this chapter

Applying what you learned in the last section of this chapter to the pocketful of functions you ve been introduced to (the identity, squaring, reciprocal, and absolute value functions), graph the following functions. Label any asymptotes and \(x\) - and \(y\) -intercepts. (a) \(f(x)=\frac{1}{x^{2}}\) (b) \(g(x)=\left|(x-1)^{2}\right|\) (c) \(h(x)=\left|x^{2}-1\right|\) (d) \(j(x)=\frac{1}{x+1}+2\) (e) \(m(x)=\frac{-1}{x-2}+1\) (f) \(p(x)=\left|\frac{1}{x}\right|\)

Find functions \(f\) and \(g\) such that \(h(x)=f(g(x))\) and neither \(f\) nor \(g\) is the identity function, i.e., \(f(x) \neq x\) and \(g(x) \neq x .\) Answers to these problems are not unique. \(h(x)=5(x-\pi)^{2}+4(x-\pi)+7\)

Let \(f(x)=x^{2}\) and \(g(x)=1 / x\). Use your knowledge of the graphs of \(f\) and \(g\) to sketch the graph of \(h(x)=f(x) \cdot g(x)\). Where is \(h(x)\) unde ned? How can you indicate this on your graph? How does your graphing calculator deal with the point at which \(h\) is unde ned?

Let \(f(x)=\frac{1}{x}+x\) and \(g(x)=\frac{2 x}{x^{2}+1} .\) Evaluate the following expressions. (a) \(g(f(2))\) (b) \(f(g(2))\)

You put $$\$ 300$$ in a bank account at \(4 \%\) annual interest compounded annually and you plan to leave it there without making any additional deposits or withdrawals. With each passing year, the amount of money in the account is \(104 \%\) of what it was the previous year. (a) Write a formula for the function \(f\) that takes as input the balance in the account at some particular time and gives as output the balance one year later. Write this formula as one term, not the sum of two terms. (b) Two years after the initial deposit is made, the balance in the account is \(f(f(300))\) and three years after, it is \(f(f(f(300)))\). Explain. (c) What quantity is given by \(f(f(f(f(300))))\) ? (d) Challenge: Write a formula for the function \(g\) that takes as input \(n\), the number of years the deposit of \(M\) dollars has been in the bank, and gives as output the balance in the account.

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