Problem 59 - Calculus and its applications

Question

Differentiate. $$ y=7 \ln |x| $$

Step-by-Step Solution

Answer

The derivative is \( \frac{7}{x} \).

Step 1: Understand the Function

We are given a function \( y = 7 \ln |x| \). The goal is to find its derivative with respect to \( x \). The expression \( \ln |x| \) signifies the natural logarithm of the absolute value of \( x \).

Step 2: Apply the Derivative Rule for Natural Logarithm

The derivative of \( \ln |u| \) with respect to \( u \) is \( \frac{1}{u} \). In this function, \( u = x \), so the derivative \( \frac{d}{dx}(\ln |x|) \) is \( \frac{1}{x} \).

Step 3: Use Constant Multiple Rule

Since the function is \( y = 7 \ln |x| \), we apply the constant multiple rule. This rule states that if you have a constant multiplier (in this case, 7), you can factor it out of the differentiation. Therefore, the derivative is \( 7 \cdot \frac{d}{dx}(\ln |x|) \).

Step 4: Simplify the Derivative

We calculated \( \frac{d}{dx}(\ln |x|) = \frac{1}{x} \). So, the derivative becomes \( 7 \cdot \frac{1}{x} = \frac{7}{x} \).

Step 5: Finalize the Solution

The derivative of the given function \( y = 7 \ln |x| \) is \( \frac{7}{x} \). Make sure to note that this derivative is valid for all non-zero \( x \).

Key Concepts

Natural Logarithm Differentiation

Understanding how to differentiate the natural logarithm function is essential in calculus. The natural logarithm, denoted as \(\ln x\), is a common logarithmic function based on the constant \(e\), which is approximately 2.71828. But what happens when you take the natural logarithm of the absolute value, \(\ln |x|\)? Let's break it down.

The absolute value \(|x|\) influences the function by ensuring that the argument inside the logarithm is always non-negative. This is because the logarithm of a negative number is undefined in the real number system.

• For positive \(x\), \(|x| = x\).
• For negative \(x\), \(|x| = -x\).

When differentiating \(\ln |x|\), we use the derivative formula: \(\frac{d}{dx}(\ln |u|) = \frac{1}{u} \frac{du}{dx}\). Here, \(u = x\) and \(\frac{du}{dx} = 1\), leading to: \[ \frac{d}{dx}(\ln |x|) = \frac{1}{x} \]This formula shows us that the derivative of the natural logarithm of \(x\) behaves nicely regardless of the sign of \(x\), as long as \(x eq 0\).

Absolute Value in Calculus

In calculus, absolute value serves an important role, especially when dealing with functions that may cross from negative to positive values. We commonly see absolute values to protect functions from undefined behavior, like taking the log of a negative number.

The absolute value function is simple yet powerful: it takes any input \(x\) and outputs its non-negative value. This means:

• \( |x| = x \), if \(x\) is positive,
• \( |x| = -x \), if \(x\) is negative.

This property comes into play when differentiating expressions that include absolute values. You need to be mindful of the domain of the function, since behaviors can shift above and below zero.

When differentiating \(\ln |x|\), absolute value ensures we're not mistakenly trying to logs of negative numbers. By maintaining \(|x|\), we rest assured that \(\ln |x|\) works for every non-zero \(x\). This adaptability is what makes calculus such a versatile tool while dealing with real-world scenarios that don’t always adhere to strict positive measures.

Constant Multiple Rule

The constant multiple rule in calculus is a straightforward yet handy tool when differentiating functions. It states that if you multiply a function by a constant, you can "carry" that constant through the differentiation process.

For example, if a function \(y\) is given as \(c \cdot f(x)\), where \(c\) is a constant, the derivative \(y'\) of the function concerning \(x\) will be \(c \cdot f'(x)\). This means you differentiate the function as usual and then multiply the result by the constant.

Applying this to our function \(y = 7 \ln |x|\), we can recognize that 7 is our constant multiplier. Thus, the derivative is computed as:

• Differentiate \(\ln |x|\) to get \(\frac{1}{x}\),
• Then multiply by 7, resulting in \(\frac{7}{x}\).

This rule simplifies the differentiation of scalar multiples of functions and is an essential part of understanding how linear scaling impacts calculus operations. Remember, this rule only applies as long as the constant does not depend on \(x\).