Understanding Exponential Functions

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Questions and Answers

Which statement accurately distinguishes between exponential and linear growth?

  • Exponential growth involves multiplying by a constant factor over equal intervals, while linear growth involves adding a constant amount. (correct)
  • Exponential growth applies only to populations, while linear growth applies only to financial investments.
  • Linear growth eventually surpasses exponential growth due to its additive nature.
  • Exponential growth involves adding a constant amount over equal intervals, while linear growth involves multiplying by a constant factor.

In the general form of an exponential function, $f(x) = ab^x$, what constraints apply to the base, $b$?

  • $b$ must be an integer.
  • $b$ must be greater than 1.
  • $b$ can be any real number.
  • $b$ must be a positive real number not equal to 1. (correct)

Consider two exponential decay functions, $f(x) = a(0.5)^x$ and $g(x) = a(0.75)^x$, with $a > 0$. Which statement accurately compares their rates of decay?

  • Both functions decay at the same rate because they are both exponential functions.
  • $f(x)$ decays faster than $g(x)$ because its base is smaller. (correct)
  • The rates of decay cannot be compared without knowing the value of $a$.
  • $g(x)$ decays faster than $f(x)$ because its base is larger.

Given an exponential function $f(x) = a \cdot b^x$ where $0 < b < 1$, which of the following transformations would result in an exponential growth function?

<p>Reflecting the function across the y-axis. (D)</p> Signup and view all the answers

How does continuous compounding differ fundamentally from compounding a finite number of times per year?

<p>Continuous compounding involves an infinite number of compounding periods, leading to the theoretical maximum growth achievable. (D)</p> Signup and view all the answers

An investment grows continuously at a nominal rate $r$. Which formula correctly calculates the percentage of interest earned relative to the principal at time $t$?

<p>$I(t) = e^{rt} - 1$ (B)</p> Signup and view all the answers

Given two exponential functions, $f(x) = a \cdot e^{kx}$ and $g(x) = a \cdot e^{-kx}$, where $a > 0$ and $k > 0$, describe the relationship between these functions.

<p>$f(x)$ represents exponential growth, while $g(x)$ represents exponential decay. (A)</p> Signup and view all the answers

If a radioactive substance decays exponentially, and its half-life is known, what information is needed to determine the remaining amount of the substance after a given time?

<p>The half-life and the initial amount of the substance are needed. (C)</p> Signup and view all the answers

Consider an investment that compounds continuously. How does the effective annual yield compare to the nominal APR?

<p>The effective annual yield is always greater than the nominal APR. (B)</p> Signup and view all the answers

In the context of exponential growth or decay, what is the significance of the natural logarithm (ln) in solving for time or rate variables?

<p>It simplifies calculations by converting exponential equations into linear equations. (A)</p> Signup and view all the answers

Flashcards

Percent Change

A change based on a percentage of the original amount.

Exponential Growth

Increase at a constant multiplicative rate of change over equal time increments.

Exponential Decay

Decrease at a constant multiplicative rate of change over equal time increments.

Exponential Growth (value)

The original value increases by the same percentage over equal increments.

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Linear Growth (value)

The original value increases by the same amount over equal increments.

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Exponential Function (General Form)

f(x) = a*b^x, where a is nonzero and b is positive and not equal to 1

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Exponential Growth Function

A function that grows at a rate proportional to its size (b > 1)

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Exponential Decay Function

A function that decreases at a rate proportional to its size (0 < b < 1)

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Nominal Interest Rate

An interest rate that is typically expressed as an annual rate.

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Compound Interest Formula

A = a(1 + r/k)^(kt), where a is the initial amount, r is the interest rate, k is the number of compounding periods per year, and t is the time in years.

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Study Notes

  • Exponential functions model rapid growth, such as population increases.

Identifying Exponential Functions

  • Linear growth involves a constant rate of change, where the output increases by a fixed number for each unit increase in input (e.g., f(x) = 3x + 4).
  • Exponential relationships involve a percent change per unit time instead of a constant change.
  • Percent change is a change based on a percentage of the original amount.
  • Exponential growth is an increase based on a constant multiplicative rate of change over equal time increments, reflecting a percent increase of the original amount over time.
  • Exponential decay is a decrease based on a constant multiplicative rate of change over equal time increments, reflecting a percent decrease of the original amount over time.
  • Exponential growth dwarfs linear growth because the original value increases by the same percentage over equal increments.
  • Linear growth sees the original value increase by the same amount over equal increments.

Defining an Exponential Function

  • The general form of an exponential function is f(x) = abË£, where a is a nonzero number and b is a positive real number not equal to 1.
  • If b > 1, the function grows at a rate proportional to its size.
  • If 0 < b < 1, the function decays at a rate proportional to its size.
  • The domain of f is all real numbers.
  • The range of f is all positive real numbers if a > 0.
  • The range of f is all negative real numbers if a < 0.
  • The y-intercept is (0, a), and the horizontal asymptote is y = 0.

Evaluating Exponential Functions

  • To evaluate an exponential function, substitute the given x-value into the function and simplify.
  • Standard form is f(x) = abË£.
  • Shifted form is f(x) = ab^(x-c) + d.

Finding the Equation of an Exponential Function

  • Given two data points, create two equations by substituting the points into the form f(x) = abË£.
  • Solve the resulting system of two equations in two unknowns (a and b) to find the equation of the exponential function.

Understanding Compound Interest

  • Principal (P) is the initial investment.
  • Annual interest rate (r) is a percentage of the principal earned per year.
  • Term (t) is the length of time over which interest is earned.
  • Compounding refers to the process of earning interest on prior interest earned, along with the principal.
  • Compound interest: A = P(1 + r/n)^(nt), where:
    • A = value of the investment after t years.
    • t = number of years.
    • P = principal.
    • r = annual interest rate.
    • n = number of times the interest is compounded per year.
  • Nominal rate is the stated interest rate, while effective rate is the actual interest rate earned after compounding.

Evaluating Exponential Functions with Base e

  • e is an irrational number approximately equal to 2.7182818284.
  • The function f(x) = eË£ is called the natural exponential function.
  • Continuous growth/decay formula: f(x) = ae^(rt), where:
    • a is the initial value.
    • r is the continuous growth rate per unit of time.
    • t is the elapsed time.
  • If r > 0, the formula represents continuous growth.
  • If r < 0, the formula represents continuous decay.
  • An exponential decay function can be written as f(x) = a(e)^(-nx) for some positive number n.

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