Problem 14
Question
Table 2.4 gives \(P=f(t),\) the number of households, in millions, in the US with cable television \(t\) years since \(1998^{4}\) (a) Does \(f^{\prime}(4)\) appear to be positive or negative? What does this tell you about the percent of households with cable television? (b) Estimate \(f^{\prime}(2) .\) Estimate \(f^{\prime}(10) .\) Explain what each is telling you, in terms of cable television. $$\begin{array}{c|c|c|c|c|c|c|c}\hline t & 0 & 2 & 4 & 6 & 8 & 10 & 12 \\\\\hline P & 64.65 & 66.25 & 66.732 & 65.727 & 65.141 & 64.874 & 60.958 \\\\\hline\end{array}$$
Step-by-Step Solution
Verified Answer
(a) Negative. Cable households decreased at t=4. (b) f'(2) ≈ 0.5205; f'(10) ≈ -1.04575. Increasing at t=2, decreasing at t=10.
1Step 1: Evaluate sign of f'(4)
To determine if \(f^{\prime}(4)\) is positive or negative, compare the values of \(f(4)\) and \(f(6)\). \(P\) decreases from \(66.732\) at \(t=4\) to \(65.727\) at \(t=6\), indicating \(f^{\prime}(4)\) is negative. This implies the number of households with cable television is decreasing at \(t=4\).
2Step 2: Estimate f'(2)
To estimate \(f^{\prime}(2)\), compute the slope of the tangent line at \(t=2\) using points \((t=0, f(0)=64.65)\) and \((t=4, f(4)=66.732)\).\[f^{\prime}(2) \approx \frac{f(4) - f(0)}{4 - 0} = \frac{66.732 - 64.65}{4} = \frac{2.082}{4} = 0.5205\]This tells us the number of households with cable was increasing at a rate of about 0.5205 million per year at \(t=2\).
3Step 3: Estimate f'(10)
To estimate \(f^{\prime}(10)\), compute the slope of the tangent line at \(t=10\) using points \((t=8, f(8)=65.141)\) and \((t=12, f(12)=60.958)\).\[f^{\prime}(10) \approx \frac{f(12) - f(8)}{12 - 8} = \frac{60.958 - 65.141}{4} = \frac{-4.183}{4} = -1.04575\]This indicates the number of households with cable was decreasing at a rate of approximately 1.04575 million per year at \(t=10\).
Key Concepts
Derivative InterpretationSlope EstimationRates of Change
Derivative Interpretation
In calculus, the derivative of a function provides crucial insight into how the function behaves at any given point. When we talk about the derivative, we are essentially referring to the rate at which one quantity changes with respect to another. This is a foundational concept in understanding real-world changes and patterns in data.
For example, in the context of the exercise, the derivative of the function \(f(t)\) represents the rate of change of the number of households with cable television with respect to time. A positive derivative indicates an increase in the number of households over time, while a negative derivative signals a decrease.
Understanding whether the derivative is positive or negative at a certain point can help infer trends. Such as, \(f^{\prime}(4)\) being negative tells us that, around the fourth year, the number of households with cable began to decline. These interpretations can guide businesses and policymakers in decision-making related to cable television distribution strategies.
For example, in the context of the exercise, the derivative of the function \(f(t)\) represents the rate of change of the number of households with cable television with respect to time. A positive derivative indicates an increase in the number of households over time, while a negative derivative signals a decrease.
Understanding whether the derivative is positive or negative at a certain point can help infer trends. Such as, \(f^{\prime}(4)\) being negative tells us that, around the fourth year, the number of households with cable began to decline. These interpretations can guide businesses and policymakers in decision-making related to cable television distribution strategies.
Slope Estimation
Estimating the slope of a function over different intervals can provide insights into how quickly or slowly a change is occurring. In applied calculus, this method is often used to predict trends and analyze scenarios over specific periods.
In the given problem, slope estimation was used to find \(f^{\prime}(2)\) and \(f^{\prime}(10)\). To estimate these, we looked at the difference in function values over the chosen intervals and calculated the average rate of change. For \(f^{\prime}(2)\), the calculation involved comparing from \(t=0\) to \(t=4\). The estimate of 0.5205 suggested that during this time, the number of households was increasing annually by approximately 0.5205 million. Conversely, \(f^{\prime}(10)\) showed a decrease of about 1.04575 million households per year between years 8 and 12.
Such estimations are vital in the context of business to foresee how trends might evolve and to plan accordingly. It simplifies complex data into manageable and interpretable information, which aids in strategic planning and forecasting.
In the given problem, slope estimation was used to find \(f^{\prime}(2)\) and \(f^{\prime}(10)\). To estimate these, we looked at the difference in function values over the chosen intervals and calculated the average rate of change. For \(f^{\prime}(2)\), the calculation involved comparing from \(t=0\) to \(t=4\). The estimate of 0.5205 suggested that during this time, the number of households was increasing annually by approximately 0.5205 million. Conversely, \(f^{\prime}(10)\) showed a decrease of about 1.04575 million households per year between years 8 and 12.
Such estimations are vital in the context of business to foresee how trends might evolve and to plan accordingly. It simplifies complex data into manageable and interpretable information, which aids in strategic planning and forecasting.
Rates of Change
Rates of change are at the heart of calculus and provide essential information about trends and shifts in real-world phenomena. A rate of change can help us understand not just the existence of change, but its direction and magnitude.
In the context of cable television households, the rates of change tell us how quickly the market is expanding or contracting. When we see \(f^{\prime}(2)\) as an increasing rate of about 0.5205 million households per year, it indicates a period of growth. On the other hand, the negative rate of \(f^{\prime}(10)\) by approximately 1.04575 million households per year marks a period of decline.
Understanding these rates allows stakeholders to set goals and develop strategies. For instance, if the decline is due to emerging technologies, companies might need to innovate to retain customers. Rates of change help in identifying such pivotal shifts in trends, ensuring that timely adaptations can be made to evolving market demands.
In the context of cable television households, the rates of change tell us how quickly the market is expanding or contracting. When we see \(f^{\prime}(2)\) as an increasing rate of about 0.5205 million households per year, it indicates a period of growth. On the other hand, the negative rate of \(f^{\prime}(10)\) by approximately 1.04575 million households per year marks a period of decline.
Understanding these rates allows stakeholders to set goals and develop strategies. For instance, if the decline is due to emerging technologies, companies might need to innovate to retain customers. Rates of change help in identifying such pivotal shifts in trends, ensuring that timely adaptations can be made to evolving market demands.
Other exercises in this chapter
Problem 14
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