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Use \(f(x)=2 x-3\) and \(g(x)=4-x^{2}\) to evaluate the expression. (a) \((f \circ g)(-2)\) (b) \((g \circ f)(-2)\)

Short Answer

Expert verified
(a) -3; (b) -45.

Step by step solution

01

Understanding Composition of Functions

The composition of two functions \(f\) and \(g\), written as \((f \circ g)(x)\), means you first apply the function \(g\) and then apply the function \(f\) to the result. So, \((f \circ g)(x) = f(g(x))\).
02

Calculate \(g(-2)\)

Calculate the value of \(g(-2)\) using the formula for \(g(x)\), which is \(g(x) = 4 - x^2\). Substitute \(-2\) into the formula: \[ g(-2) = 4 - (-2)^2 = 4 - 4 = 0. \]
03

Calculate \(f(g(-2))\)

Since \(g(-2) = 0\), you now calculate \(f(0)\) using the formula for \(f(x)\), which is \(f(x) = 2x - 3\). Substitute \(0\) into the formula: \[ f(0) = 2(0) - 3 = -3. \]
04

Conclusion for \((f \circ g)(-2)\) result

The result of the composition \((f \circ g)(-2)\) is \(-3\). This is obtained after calculating \(f(g(-2)) = f(0) = -3\).
05

Calculate \(f(-2)\)

For part (b), calculate the value of \(f(-2)\) using \(f(x) = 2x - 3\). Substitute \(-2\) into the formula: \[ f(-2) = 2(-2) - 3 = -4 - 3 = -7. \]
06

Calculate \(g(f(-2))\)

Now use the result from the previous step, \(f(-2) = -7\), to calculate \(g(-7)\) using \(g(x) = 4 - x^2\). Substitute \(-7\) into the formula: \[ g(-7) = 4 - (-7)^2 = 4 - 49 = -45. \]
07

Conclusion for \((g \circ f)(-2)\) result

The result of the composition \((g \circ f)(-2)\) is \(-45\). This is obtained after calculating \(g(f(-2)) = g(-7) = -45\).

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Key Concepts

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

Precalculus
Precalculus is the mathematical foundation that prepares students for the study of calculus. It bridges the concepts and provides the tools necessary to tackle more advanced topics. In precalculus, students learn about various functions, their properties, and how they can be manipulated. The primary focus is on preparing the student for understanding more complex algebra and trigonometry.

The subject includes topics like functions, equations, complex numbers, and vectors. Understanding precalculus is crucial because it sets the stage for calculus, where you will encounter limits, derivatives, and integrals. Mastery of precalculus ensures you're equipped with the analytical skills necessary to succeed in calculus.
Evaluating Functions
Evaluating functions involves finding the output of a function given an input. This process helps in understanding how functions behave and what kind of transformations they display. The basic idea is to replace the variable in the function's formula with a given number or expression.

For example, evaluating the function \(f(x)=2x-3\) at \(x=-2\) involves substituting \(x\) with \(-2\) and calculating the result, which would be \(f(-2) = 2(-2) - 3 = -4 - 3 = -7\). It's important to carefully substitute and simplify correctly to avoid errors.
  • Step 1: Substitute the input value into the function.
  • Step 2: Perform the arithmetic operations.
  • Step 3: Simplify the result to obtain the output.
Understanding how to evaluate functions provides insight into their structure and how they respond to different inputs.
Composite Functions
Composite functions are formed when two functions combine to create a new function. This is indicated by symbols like \(f \circ g\) for function composition, which means applying one function to the results of another. The notation \(f \circ g(x) = f(g(x))\) shows the order of operations: first apply \(g\), then \(f\) on the result.

Understanding composite functions is critical as it allows complex problems to be broken down into simpler parts. For example, with \(f(x)=2x-3\) and \(g(x)=4-x^2\), to find \(f \circ g(-2)\), you first compute \(g(-2)\) and then use that output as input for \( f(\).
  • Step 1: Compute the inner function.
  • Step 2: Use the result as the input for the outer function.
  • Step 3: Simplify to find the final output.
This approach simplifies problem-solving by handling each function individually before combining them into a single process.
Mathematics for Calculus
Mathematics for calculus involves learning and understanding various mathematical principles that are fundamental for grasping calculus concepts. This includes not only precalculus but also concepts like limits and continuity, which are pivotal in calculus.

Calculus demands a strong understanding of how functions operate, how they can be combined, and how they behave as values approach certain limits. Skills from precalculus, like manipulating and evaluating functions, directly transfer to calculus as they form the foundation for understanding derivatives and integrals.
  • Limits: Understanding approaching values.
  • Derivatives: Rate of change and slope of curves.
  • Integrals: Area under a curve.
Mathematics for calculus equips students with the tools and ways of thinking necessary for tackling the complex topics of calculus harmoniously.

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Most popular questions from this chapter

As a weather balloon is inflated, the thickness \(T\) of its rubber skin is related to the radius of the balloon by $$T(r)=\frac{0.5}{r^{2}}$$ where \(T\) and \(r\) are measured in centimeters. Graph the function \(T\) for values of \(r\) between 10 and \(100 .\)

DISCUSS: Finding an Inverse "in Your Head" In the margin notes in this section we pointed out that the inverse of a function can be found by simply reversing the operations that make up the function. For instance, in Example 7 we saw that the inverse of $$f(x)=3 x-2 \quad \text { is } \quad f^{-1}(x)=\frac{x+2}{3}$$ because the "reverse" of "Multiply by 3 and subtract 2" is "Add 2 and divide by 3 ". Use the same procedure to find the inverse of the following functions. (a) \(f(x)=\frac{2 x+1}{5}\) (b) \(f(x)=3-\frac{1}{x}\) (c) \(f(x)=\sqrt{x^{3}+2}\) (d) \(f(x)=(2 x-5)^{3}\) Now consider another function: $$f(x)=x^{3}+2 x+6$$ Is it possible to use the same sort of simple reversal of operations to find the inverse of this function? If so, do it. If not, explain what is different about this function that makes this task difficult.

Determine whether the equation defines \(y\) as a function of \(x .\) (See Example 9.) $$x^{2}+(y-1)^{2}=4$$

Sketch graphs of the functions \(f(x)=\|x\|, g(x)=\|2 x\|,\) and \(h(x)=\|3 x\|\) on separate graphs. How are the graphs related? If \(n\) is a positive integer, what does a graph of \(k(x)=\|n x\|\) look like?

A savings account earns \(5 \%\) interest compounded annually. If you invest \(x\) dollars in such an account, then the amount \(A(x)\) of the investment after one year is the initial investment plus \(5 \% ;\) that is, $$A(x)=x+0.05 x=1.05 x$$ Find $$\begin{aligned} &A \circ A\\\&A \circ A \circ A\\\&A \circ A \circ A \circ A\end{aligned}$$ What do these compositions represent? Find a formula for what you get when you compose \(n\) copies of \(A\).

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