Problem 12 - Calculus and its applications

Question

Differentiate. $$ f(x)=e^{-x} $$

Step-by-Step Solution

Answer

The derivative is \( f'(x) = -e^{-x} \).

Step 1: Identify the Rule of Differentiation

To differentiate the function \( f(x) = e^{-x} \), we first identify the rule of differentiation applicable. Here, we apply the chain rule because we have an exponential function with a composite exponent \(-x\). The derivative of \( e^u \) with respect to \( u \) is \( e^u \), while the derivative of \(-x\) with respect to \( x \) is \(-1\).

Step 2: Apply the Chain Rule

Using the chain rule, the derivative \( f'(x) \) is found by differentiating the outer function and multiplying it by the derivative of the inner function: \[ f'(x) = e^{-x} \cdot (-1) \]

Step 3: Simplify the Expression

Simplify the expression obtained by applying the chain rule. The derivative of \( e^{-x} \) becomes: \[ f'(x) = -e^{-x} \]

Key Concepts

Chain Rule in Differentiation

The chain rule is a fundamental tool in calculus used to differentiate composite functions. A composite function is essentially a function within another function, often represented as \( f(g(x)) \). The chain rule allows us to take derivatives of these complex functions by breaking them down into their simpler components. When using the chain rule, you differentiate the outer function first and then multiply by the derivative of the inner function.

For example, if you have a function like \( f(x) = e^{-x} \), you identify two distinct parts:

• The outer function: \( e^u \)
• The inner function: \( u = -x \)

Now, the chain rule directs us to:

- Differentiate the outer function considering the inner function as a variable. So, the derivative of \( e^u \) is \( e^u \).
- Multiply this by the derivative of the inner function: the derivative of \(-x\) is \(-1\).

Thus, for \( f(x) = e^{-x} \), applying the chain rule results in multiplying \( e^{-x} \) by \(-1\), giving us a final derivative of \(-e^{-x} \).

Exponential Function Characteristics

Understanding an exponential function is crucial in calculus, especially since they frequently appear in various scientific applications. The general form of an exponential function is \( f(x) = a^x \). However, when the base is Euler's number \( e \), it becomes \( f(x) = e^x \), a special type of exponential function that is particularly nice to differentiate.

When differentiating an exponential function like \( e^x \), it's important to note:

• The derivative of \( e^x \), interestingly, is itself \( e^x \).
• This self-replicating property showcases the distinct and unique nature of the exponential function.

The situation changes slightly when the exponent itself is more complex. For functions like \( e^{-x} \), you need to apply the chain rule, as discussed, because of the composite nature of the exponent.

Exponential functions widely appear in natural growth processes, compounding interest, and in fields like physics and biology, as they represent processes with constant relative growth rates. Understanding their differentiation helps tackle many real-world problems smoothly.

Understanding Derivatives

Derivatives lie at the heart of calculus, acting as a measure of how a function changes as its input changes. At its core, the derivative of a function at a given point reflects the rate of change or the slope of the tangent line at that point.

The act of differentiating involves calculating this instantaneous rate of change. For any function \( f(x) \), the derivative \( f'(x) \) informs us about how \( f(x) \) changes with a small change in \( x \).

When differentiating different types of functions, several rules and techniques, like the chain rule, make the process streamlined. In our particular function, \( f(x) = e^{-x} \), the chain rule plays a crucial role in simplifying the derivative calculation.

• Identifying when a chain rule is required, such as in composite functions, is a vital calculus skill.
• Once differentiated correctly, the derivative \( f'(x) = -e^{-x} \) serves as a tool to understand the decreasing nature and slope dynamics of the original function.

Derivatives are essential in various fields, including physics for motion and dynamics, economics for understanding marginal concepts, and engineering for design and analysis. Grasping the basics of derivatives opens the door to more advanced topics in calculus.