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Let \(f(x)=2 x+3\) and \(g(x)=x^{3} .\) Find the indicated quantity. a. \((g \circ f)(1)\) b. \((g \circ f)(-2)\)

Short Answer

Expert verified
\((g \circ f)(1) = 125\) and \((g \circ f)(-2) = -1\).

Step by step solution

01

Understand Composition of Functions

The notation \(g \circ f\)(x) refers to the composition of functions, where \(f(x)\) is evaluated first and then the result is used as the input for \(g(x)\). In this case, evaluate \(f(x)\) at the given value, and then use that output to find the value of \(g\).
02

Evaluate \(f(x)\) at \(x = 1\)

First, substitute \(x = 1\) into \(f(x) = 2x + 3\): \(f(1) = 2(1) + 3 = 2 + 3 = 5\).
03

Evaluate \(g(x)\) using the result from Step 2

Use the result from Step 2 as the input for \(g(x) = x^3\). Thus, \(g(f(1)) = g(5) = 5^3 = 125\).
04

Compute \((g \circ f)(1)\)

The computation from Steps 2 and 3 indicates that \( (g \circ f)(1) = 125 \).
05

Evaluate \(f(x)\) at \(x = -2\)

Now substitute \(x = -2\) into \(f(x) = 2x + 3\): \(f(-2) = 2(-2) + 3 = -4 + 3 = -1\).
06

Evaluate \(g(x)\) using the result from Step 5

Use the result from Step 5 as the input for \(g(x) = x^3\). Thus, \(g(f(-2)) = g(-1) = (-1)^3 = -1\).
07

Compute \((g \circ f)(-2)\)

The computation from Steps 5 and 6 indicates that \( (g \circ f)(-2) = -1 \).

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Key Concepts

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

Algebra
Algebra is a fundamental branch of mathematics that deals with symbols and the rules for manipulating these symbols. These symbols represent numbers and quantities in equations and expressions. In this context, we're working with functions, which are algebraic expressions that relate an input to an output. Here, we have two functions:
  • For the function \(f(x) = 2x + 3\), it's a linear function. Meaning, it graphs as a straight line and represents the rule to multiply \(x\) by 2 and then add 3.
  • The function \(g(x) = x^3\) is a cubic function. This implies the output is the cube of the input value \(x\).
When solving these algebraic problems, the goal is to determine the value of composed functions at specific input values. This involves substituting values into each function and systematically working through the expression. Understanding how to work these algebraic manipulations is core to solving function composition problems.
Calculus
Calculus, although not directly used in this problem, provides valuable insights into the behavior and analysis of functions. Function composition, as seen here, is crucial for calculus concepts such as derivatives and integrals. When you evaluate a composed function like \((g \circ f)(x)\), knowing that you apply one function to the results of another forms the groundwork for more advanced calculus operations like the chain rule.When studying calculus, understanding how to "compose" a derivative using the chain rule is very similar to what we do when computing the algebraic expressions in function compositions in algebra. In our example:
  • Calculating \((g \circ f)(1)\) involves differentiating \(g(f(x))\) when we go into calculus.
  • The composition tells us how to input into one function and take that output into another, similar to differentiating composed functions.
Though calculus takes composition to further depths, seeing them in algebra lays the groundwork for understanding the behavior of functions at a more analytical level.
Mathematical Notation
Mathematical notation gives us a universal language to express mathematical ideas and operations concisely and accurately. In this exercise, we have several notations at work:
  • The notation \(f(x)\) is read as "\(f\) of \(x\)" and represents a function \(f\) applied to \(x\). In this case, \(f(x) = 2x + 3\).
  • Similarly, \(g(x)\) is "\(g\) of \(x\)" corresponding to the function \(g(x) = x^3\).
  • The composition notation \((g \circ f)(x)\) is read as "\(g\) composed with \(f\) of \(x\)". It indicates that you first calculate \(f(x)\) and then use this result as input for \(g(x)\).
  • This two-step notation is crucial for calculating the exact value of the composed function at specific inputs, as shown in the exercise.
Understanding these notational conventions helps in navigating through more complex problems with confidence and clarity. It allows one to translate mathematical language into visual representations like graphs and further mathematical operations.

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Most popular questions from this chapter

Suzuki and Kaiser \(^{43}\) estimated the demand equation for rice in Japan to be \(p=1,195,789-\) \(0.1084753 x,\) where \(x\) is in tons of rice and \(p\) is in yen per ton. Graph this equation. In \(1995,\) the quantity of rice consumed in Japan was 8,258,000 tons. According to the demand equation, what was the price in yen per ton?

You are given a pair of functions, \(f\) and \(g .\) In each case, use your grapher to estimate the domain of \((g \circ f)(x)\). Confirm analytically. $$ f(x)=x^{2}, g(x)=\sqrt{x} $$

Diamond and colleagues \(^{90}\) studied the growth habits of the Atlantic croaker, one of the most abundant fishes of the southeastern United States. The mathematical model that they created for the ocean larva stage was given by the equation $$L(t)=0.26 e^{2.876\left[1-e^{-0.0623 t}\right]}$$ where \(t\) is age in days and \(L\) is length in millimeters. Graph this equation. Find the expected age of a 3 -mm-long larva algebraically.

In a report of the Federal Trade Commission \((\mathrm{FTC})^{41}\) an example is given in which the Portland, Oregon, mill price of 50,000 board square feet of plywood is \(\$ 3525\) and the rail freight is \(\$ 0.3056\) per mile. a. If a customer is located \(x\) rail miles from this mill, write an equation that gives the total freight \(f\) charged to this customer in terms of \(x\) for delivery of 50,000 board square feet of plywood. b. Write a (linear) equation that gives the total \(c\) charged to a customer \(x\) rail miles from the mill for delivery of 50,000 board square feet of plywood. Graph this equation. c. In the FTC report, a delivery of 50,000 board square feet of plywood from this mill is made to New Orleans, Louisiana, 2500 miles from the mill. What is the total charge?

Find \(\frac{f(x+h)-f(x)}{h}\) for the indicated functions. $$ f(x)=3 x^{2}+1 $$

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