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Calculators that perform exponential regression often use \(y=a \cdot b^{x}\) as the exponential growth model instead of \(y=a \cdot e^{c x} .\) For what value of \(c\) is \(a \cdot b^{x}=a \cdot e^{c x} ?\) If a calculator gives \(y=500(1.036)^{x}\) for a growth model, then what is the continuous growth rate to the nearest hundredth of a percent?

Short Answer

Expert verified
The continuous growth rate to the nearest hundredth of a percent is approximately 3.53%.

Step by step solution

01

Understand the exponential models

There are two models given in the problem: the general exponential growth model, which is \(y = a \cdot b^{x}\), and the continuous exponential growth model, which is \(y = a \cdot e^{cx}\). We need to find the relationship between these models.
02

Set the equations equal to each other

The problem asks us for the value of \(c\) such that \(a \cdot b^{x} = a \cdot e^{cx}\). Since the equations are equal for all \(x\), the bases must also be equal for the exponent part. So, we have: \(b^{x} = e^{cx}\).
03

Isolate the exponents

For \(b^{x} = e^{cx}\) to hold true for all \(x\), the exponents of \(b\) and \(e\) must be equal. This implies that \(b = e^{c}\).
04

Solve for \(c\)

To find \(c\), take the natural logarithm of both sides: \(\text{ln}(b) = \text{ln}(e^{c})\). This simplifies to \(\text{ln}(b) = c\), giving us \(c = \text{ln}(b)\).
05

Apply the formula with the given values

The calculator gives the growth model \(y = 500(1.036)^{x}\). Here, \(b = 1.036\). Using the formula from the previous step, we get \(c = \text{ln}(1.036)\).
06

Calculate the value of \(c\)

Use a calculator to find \(c = \text{ln}(1.036)\). After calculating, \(c \approx 0.035321\).
07

Convert \(c\) to a percentage

\(c\) represents the continuous growth rate. To express it as a percentage, multiply by 100: \(0.035321 \times 100 \approx 3.53\text{\textpercent}\).

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Key Concepts

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

continuous growth rate
When we talk about exponential growth, we often use the term 'continuous growth rate' to describe how rapidly a quantity increases over time. In mathematics, this is often represented by the constant 'c' in the equation \(y = a \cdot e^{cx}\). The continuous growth rate is especially useful because it allows us to express growth in a more natural and intuitive way. For example, if we have a continuous growth rate of 3.53%, it means that the quantity grows by 3.53% every single time unit, no matter how small that unit is. This is different from, say, an annual growth rate, which only applies to a specific time period.
natural logarithm
The natural logarithm, often denoted as \(\ln\), is a mathematical function that helps us to solve problems involving exponential growth and decay. When we work with equations involving exponential functions like \(y = a \cdot e^{cx}\) or \(y = a \cdot b^{x}\), taking the natural logarithm allows us to isolate the exponent. For example, if we want to find the value of 'c' in the equation \(b = e^{c}\), we take the natural logarithm of both sides to get \(\ln(b) = c\). The natural logarithm is special because it uses the base 'e', which is approximately 2.71828. Base 'e' often appears in continuous growth or decay processes, making \(\ln\) a very powerful tool in science and engineering.
exponential regression
Exponential regression is a statistical method used to fit an exponential model to a set of data points. This is especially useful when the data suggests a rapid increase or decrease. In exponential regression, we typically look for a model of the form \(y = a \cdot b^{x}\). By using regression techniques, we can determine the values of 'a' and 'b' that best fit the data. Once we have these values, we can make predictions about future behavior. For instance, if a calculator gives the growth model \(y = 500(1.036)^{x}\), it means that 'a' is 500 and 'b' is 1.036. This can then be transformed into the continuous growth model \(y = 500 \cdot e^{0.035321x}\) by finding the corresponding 'c' using the natural logarithm.
base e
Base 'e', also known as Euler's number, is approximately equal to 2.71828. It is a fundamental constant in mathematics, and it appears frequently in problems involving exponential growth and continuous compounding. When we use 'e' as a base in exponential functions, we can write equations in the form of \(y = a \cdot e^{cx}\). This form is particularly useful because it simplifies many mathematical processes, such as differentiation and integration. For example, when we convert the growth model from \(y = a \cdot b^{x}\) to \(y = a \cdot e^{cx}\), finding the value of 'c' involves using the natural logarithm, since \(c = \ln(b)\). This transformation makes it easier to analyze and interpret the growth rate in many scientific and engineering applications.

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Most popular questions from this chapter

To evaluate an exponential or logarithmic function we simply press a button on a calculator. But what does the calculator do to find the answer? The next exercises show formulas from calculus that are used to evaluate \(e^{x}\) and \(\ln (1+x)\). Infinite Series for \(e^{x}\) The following formula from calculus is used to compute values of \(e^{x}\) : $$e^{x}=1+x+\frac{x^{2}}{2 !}+\frac{x^{3}}{3 !}+\frac{x^{4}}{4 !}+\cdots+\frac{x^{n}}{n !}+\cdots$$ where \(n !=1 \cdot 2 \cdot 3 \cdot \cdots \cdot n\) for any positive integer \(n .\) The notation \(n !\) is read " \(n\) factorial." For example, \(3 !=1 \cdot 2 \cdot 3=6\) In calculating \(e^{x},\) the more terms that we use from the formula, the closer we get to the true value of \(e^{x}\). Use the first five terms of the formula to estimate the value of \(e^{0.1}\) and compare your result to the value of \(e^{0.1}\) obtained using the \(e^{x}-\) key on your calculator.

Solve each problem. When needed, use 365 days per year and 30 days per month. Working by the Hour One million dollars is deposited in an account paying \(6 \%\) compounded continuously. a. What amount of interest will it earn in its first hour on deposit? Hint One hour is \(1 / 8760\) of a year. b. What amount of interest will it earn during its 500 th hour on deposit? Hint Subtract the amount for \(t=499\) from the amount for \(t=500\)

Solve each problem. When needed, use 365 days per year and 30 days per month. National Debt The national debt was about \(\$ 10\) trillion in 2008 - a. If the United States paid \(5.5 \%\) interest compounded continuously on the debt, then what amount of interest does the government pay in one day? b. How much is saved in one day if the interest were \(5.5 \%\) compounded daily?

Present Value of a \(\mathrm{CD}\) What amount (present value) must be deposited today in a certificate of deposit so that the investment will grow to \(\$ 20,000\) in 18 years at \(6 \%\) compounded continuously.

Room Temperature Marlene brought a can of polyurethane varnish that was stored at \(40^{\circ} \mathrm{F}\) into her shop, where the temperature was \(74^{\circ} .\) After 2 hr the temperature of the varnish was \(58^{\circ} .\) If the varnish must be \(68^{\circ}\) for best results, then how much longer must Marlene wait until she uses the varnish?

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