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Ch. 7 - Logarithmic, Exponential Functions, and Hyperbolic Functions
Briggs - Calculus: Early Transcendentals 3rd Edition
Briggs3rd EditionCalculus: Early TranscendentalsISBN: 9780136847243Non è quello che usi tu?Cambia libro di testo
Capitolo 7, Problema 7.RE.20a

Population growth The population of a large city grows exponentially with a current population of 1.3 million and a predicted population of 1.45 million 10 years from now.


a. Use an exponential model to estimate the population in 20 years. Assume the annual growth rate is constant.

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1
Identify the exponential growth model formula: \(P(t) = P_0 \cdot e^{rt}\), where \(P(t)\) is the population at time \(t\), \(P_0\) is the initial population, \(r\) is the growth rate, and \(t\) is the time in years.
Assign the known values: initial population \(P_0 = 1.3\) million, population after 10 years \(P(10) = 1.45\) million, and \(t = 10\) years.
Use the known values to set up the equation \(1.45 = 1.3 \cdot e^{10r}\) and solve for the growth rate \(r\) by isolating \(r\).
Once \(r\) is found, use the exponential model again to estimate the population after 20 years by calculating \(P(20) = 1.3 \cdot e^{20r}\).
Interpret the result as the estimated population in millions after 20 years, based on the constant annual growth rate.

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Exponential Growth Model

Exponential growth describes a process where the quantity increases at a rate proportional to its current value, modeled by P(t) = P_0 * e^(rt). Here, P_0 is the initial population, r is the growth rate, and t is time. This model is essential for predicting future population sizes when growth is continuous and constant.
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Exponential Growth & Decay

Determining the Growth Rate

To use the exponential model, the growth rate r must be found from known data points. Given initial and future populations at specific times, r can be calculated by rearranging the formula: r = (1/t) * ln(P(t)/P_0). This step is crucial to accurately estimate future populations.
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Intro To Related Rates

Using the Model for Prediction

Once the growth rate is known, the exponential model can predict population at any future time by substituting t into P(t) = P_0 * e^(rt). This allows estimation of the population after 20 years, assuming the growth rate remains constant over time.
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Using The Acceleration Function