Problem 23 - Applied Calculus

Question

In the form \(P=P_{0} a^{t}\). Which represent exponential growth and which represent exponential decay? $$P=15 e^{0.25 t}$$

Step-by-Step Solution

Answer

Exponential growth, since base is greater than 1.

Step 1: Identify the form of the exponential function

The given exponential function is \( P = 15 e^{0.25 t} \). Identify the structure of this equation relative to the standard form \( P = P_0 a^t \). Here, \( P_0 = 15 \), \( a = e^{0.25} \), and \( t \) represents time.

Step 2: Determine the value of base 'a'

Calculate the value of \( a \) which is \( e^{0.25} \). It is important to know that \( e \) is a constant approximately equal to 2.718. Consequently, \( a = e^{0.25} > 1 \) because any positive power of \( e \) is greater than 1.

Step 3: Identify type of exponential function

With \( a = e^{0.25} > 1 \), the function \( P = 15 e^{0.25 t} \) represents exponential growth. This is because the base \( a \) is greater than 1, indicating that \( P \) increases as time \( t \) increases.

Key Concepts

Exponential Function

An exponential function is a powerful mathematical equation commonly used to model real-world phenomena. It is characterized by a constant base raised to the power of a variable exponent. The general form of an exponential function can be written as \( P = P_0 a^t \), where:

• \( P_0 \) is the initial value or starting amount.
• \( a \) is the base of the exponential function.
• \( t \) is the variable representing time or any other independent variable.

Exponential functions are used to model situations where growth or decay accelerates rapidly. Understanding the structure of the exponential function is crucial to identifying whether a situation involves exponential growth or decay. The main clue lies in the value of the base \( a \).

Base of Exponential Function

The base of an exponential function, denoted by \( a \), plays a vital role in determining the behavior of the function. The number \( e \) which is approximately 2.718, is often used as a base. This number is known as Euler's number and is a fundamental constant in mathematics. If \( a \) is greater than 1, the function signifies exponential growth, while if \( a \) is between 0 and 1, it represents exponential decay. To clarify:

• When \( a > 1 \), the function grows as time increases because each increase in \( t \) multiplies \( P_0 \) by a number greater than one, amplifying its effect.
• When \( 0 < a < 1 \), the function shrinks as time progresses since the growth factor reduces \( P_0 \) at every step.

In our example, \( a = e^{0.25} \), which is greater than 1, indicating exponential growth.

Exponential Growth

Exponential growth occurs when a quantity increases at a rate proportional to its current value, leading to the rapid escalation of that quantity over time. This is evident in contexts such as population growth, compound interest, or the spread of a virus. The defining characteristic in exponential growth is that the rate of increase becomes progressively faster, creating a curve that skyrockets as time goes on. In the equation \( P = 15 e^{0.25 t} \), the base \( e^{0.25} > 1 \), demonstrating an increase of \( P \) over time \( t \). This means that as time progresses, the value of \( P \) grows exponentially rather than steadily. An important takeaway is the larger the exponent, the faster the growth rate, transforming subtle early increases into significant later rises. Understanding exponential growth helps predict future values from past and current data, which is critical in decision-making processes ranging from business to environmental science.