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Find the instantaneous rates of change of the given functions at the indicated points. \(f(x)=-2 x^{2}+3, c=2\)

Short Answer

Expert verified
The instantaneous rate of change at \( x = 2 \) is \( -8 \).

Step by step solution

01

Understand the Problem

The problem asks for the instantaneous rate of change of the function \( f(x) = -2x^2 + 3 \) at the point \( x = c = 2 \). This means we need to find the derivative of the function and evaluate it at \( x = 2 \).
02

Find the Derivative

We apply the power rule of derivatives. For the function \( f(x) = -2x^2 + 3 \), the derivative \( f'(x) \) is found as follows:\[ f'(x) = \frac{d}{dx}(-2x^2) + \frac{d}{dx}(3) = -4x + 0 \]Thus, \( f'(x) = -4x \).
03

Evaluate the Derivative at x = 2

Now that we have \( f'(x) = -4x \), we substitute \( x = 2 \):\[ f'(2) = -4(2) = -8 \]
04

Interpret the Result

The instantaneous rate of change of \( f(x) \) when \( x = 2 \) is \( -8 \). This means that at \( x = 2 \), the function \( f(x) = -2x^2 + 3 \) is decreasing at a rate of 8 units per unit increase in \( x \).

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Key Concepts

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

Understanding Derivatives
Derivatives are a fundamental concept in calculus, helping us understand how functions change. When you hear the term derivative, think of it as a mathematical way to measure how a function is behaving at any given point. It tells us the rate at which the function is changing with respect to one of its variables. - In the context of our exercise, the derivative represents the instantaneous rate of change of the function \( f(x) = -2x^2 + 3 \).- Calculating the derivative allows us to understand how quickly or slowly the function's value changes as \( x \) changes.Imagine driving a car: the speedometer shows the instantaneous speed at which the car is traveling at a given moment. Similarly, the derivative gives us the instantaneous rate of change of the function. The process of finding this derivative involves differentiation, which is key to solving many problems in calculus.
Applying the Power Rule
The power rule is a straightforward and widely used method to find derivatives of functions involving powers of \( x \). The rule states that if you have a function of the form \( f(x) = ax^n \), then its derivative \( f'(x) \) is given by \( a \cdot n \cdot x^{n-1} \). This rule significantly simplifies the process of finding derivatives for polynomial functions.- In our problem, we applied the power rule to the function \( -2x^2 \). - According to the power rule, the derivative of \( -2x^2 \) is \( -4x \), because we multiply \(-2\) (the coefficient) by \(2\) (the exponent), and reduce the power of \(x\) by one.Remember, constants like \(3\) in \( f(x) = -2x^2 + 3 \) have a derivative of zero because they do not change as \(x\) changes. Thus, the derivative of a constant is always zero. Using the power rule helps you quickly tackle similar polynomial expressions in calculus.
Interpreting Derivatives in Context
Once we find a derivative, it's important to understand what it tells us about a function's behavior. In the example problem, the derivative \( f'(x) = -4x \) evaluates to \( -8 \) when \( x = 2 \). This value of \(-8\) is significant and conveys meaningful information about the function.- The negative sign in \(-8\) indicates the function is decreasing at \( x = 2 \).- The magnitude of \(8\) tells us the rate of decrease, meaning for every unit increase in \( x \), the function's value decreases by 8 units.Understanding the interpretation of derivatives is crucial, especially in real-world applications, as it describes how systems or situations change over time. Whether evaluating speed, assessing economic trends, or analyzing physical properties like temperature or pressure, derivatives provide insight into the dynamic behavior of these systems.

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Most popular questions from this chapter

Economic Growth and the Environment Grossman and Krueger \(^{41}\) studied the relationship in a variety of countries between per capita income and various environmental indicators. The object was to determine whether environmental quality deteriorates steadily with growth. They found that the equation $$ y=f(x)=0.27 x^{3}-6.31 x^{2}+39.87 x+34.78 $$ approximated the relationship between \(x\) given as GDP per capita income in thousands of dollars and \(y\) given as units of smoke in cities. Graph on your computer or graphing calculator using a screen with dimensions [0,9.4] by \([0,150] .\) Have your computer or graphing calculator draw tangent lines to the curve when \(x\) is \(2,3,5,\) and \(6 .\) Note the slope, and relate this to the rate of change. Interpret what each of these numbers means. On the basis of this model. determine whether environmental quality deteriorates with economic growth.

Corn Yield per Acre Atwood and Helmers \(^{33}\) studied the effect of nitrogen fertilizer on corn yields in Nebraska. Nitrate contamination of groundwater in Nebraska has become such a serious problem that actions such as nitrogen rationing and taxation are under consideration. Nitrogen fertilizer is needed to increase yields, but an excess of nitrogen has been found not to help increase yields. Atwood and Helmers created a mathematical model given approximately by the equation \(Y(N)=59+\) \(0.8 N-0.003 N^{2},\) where \(N\) is the amount of fertilizer in pounds per acre and \(Y\) is the yield in bushels per acre. Graph this equation on the interval \([50,200] .\) Find the instantaneous rate of change of yield with respect to the amount of fertilizer when (a) \(N=100\) (common rate), (b) \(N=200 .\) Give units and interpret your answer.

Explain the difference between requiring a function \(f(x)\) to be continuous at \(x=a\) and requiring \(\lim f(x)\) to exist.

Economic Growth and the Environment Grossman and Krueger \(^{45}\) studied the relationship in a variety of countries between per capita income and various environmental indicators. The object was to see if environmental quality deteriorates steadily with growth. The table gives the data they collected relating the units \(y\) of coliform in waters to the GDP per capita income \(x\) in thousands of dollars. $$ \begin{array}{c|ccccccc} x & 1 & 3 & 5 & 7 & 9 & 11 & 13 \\ \hline y & 1.8 & 2.8 & 2.5 & 3.7 & 1 & 3.5 & 6 \end{array} $$ a. Use cubic regression to find the best-fitting cubic to the data and the correlation coefficient. b. Graph on your graphing calculator or computer using a screen with dimensions [0,14.1] by \([0,5] .\) Have your grapher draw tangent lines to the curve when \(x\) is 1.5 , \(2.7,3.9,6,8.4,9.6,\) and \(12 .\) Note the slope, and relate this to the rate of change. Interpret what each of these numbers means. On the basis of this model, describe what happens to the rate of change of coliform as income increases.

If the side of a cube decreases from 10 feet to 9.6 feet, use the linear approximation formula to estimate the change in volume. Use a computer or graphing calculator to estimate any slope that you need.

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