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Question

What is the derivative of e xwith respect to x e?

This question was previously asked in
NDA I 2021 GAT Previous Year Paper (18-Apr-2021)
The correct answer is \(\dfrac{xe^x}{ex^e}\)

Understanding the Calculus Problem: Derivative with Respect to a Function

The question asks for the derivative of one function (\(e^x\)) with respect to another function (\(x^e\)). This is different from the standard derivative with respect to the variable \(x\). When we need to find the derivative of a function \(y\) with respect to another function \(u\), we can use the formula derived from the chain rule:

Let \(y = f(x)\) and \(u = g(x)\). We want to find \(\frac{dy}{du}\). We can express this as: \[ \frac{dy}{du} = \frac{\frac{dy}{dx}}{\frac{du}{dx}} \]

In this specific problem, we have:

  • \(y = e^x\)
  • \(u = x^e\)

We need to calculate the derivative of \(y\) with respect to \(x\) (\(\frac{dy}{dx}\)) and the derivative of \(u\) with respect to \(x\) (\(\frac{du}{dx}\)), and then divide the first by the second.

Step-by-Step Solution to Find the Derivative

Step 1: Find the derivative of \(y = e^x\) with respect to \(x\)

The derivative of the exponential function \(e^x\) with respect to \(x\) is a standard differentiation formula.

\[ \frac{dy}{dx} = \frac{d}{dx}(e^x) \] \[ \frac{dy}{dx} = e^x \]

Step 2: Find the derivative of \(u = x^e\) with respect to \(x\)

The function \(u = x^e\) is a power function where the base is the variable \(x\) and the exponent is a constant (\(e\) is a mathematical constant, approximately 2.718). The power rule for differentiation states that the derivative of \(x^n\) with respect to \(x\) is \(nx^{n-1}\), where \(n\) is a constant.

Applying the power rule with \(n=e\):

\[ \frac{du}{dx} = \frac{d}{dx}(x^e) \] \[ \frac{du}{dx} = e \cdot x^{e-1} \]

Step 3: Calculate the derivative of \(y\) with respect to \(u\)

Now we use the formula \(\frac{dy}{du} = \frac{\frac{dy}{dx}}{\frac{du}{dx}}\). Substitute the derivatives we found in Step 1 and Step 2:

\[ \frac{dy}{du} = \frac{e^x}{ex^{e-1}} \]

Step 4: Simplify the expression

The expression we obtained is \(\frac{e^x}{ex^{e-1}}\). We can rewrite \(x^{e-1}\) using the property of exponents \(a^{m-n} = \frac{a^m}{a^n}\).

\[ x^{e-1} = \frac{x^e}{x^1} = \frac{x^e}{x} \]

Now substitute this back into the expression for \(\frac{dy}{du}\):

\[ \frac{dy}{du} = \frac{e^x}{e \cdot \left(\frac{x^e}{x}\right)} \] \[ \frac{dy}{du} = \frac{e^x}{\frac{ex^e}{x}} \]

To divide by a fraction, we multiply by its reciprocal:

\[ \frac{dy}{du} = e^x \cdot \frac{x}{ex^e} \] \[ \frac{dy}{du} = \frac{xe^x}{ex^e} \]

This is the final simplified derivative of \(e^x\) with respect to \(x^e\).

Comparing the Result with Options

Let's compare our derived result, \(\dfrac{xe^x}{ex^e}\), with the given options:

Option Expression Matches our result?
1 \(\dfrac{xe^x}{ex^e}\) Yes
2 \(\dfrac{e^x}{x^e}\) No
3 \(\dfrac{xe^x}{x^e}\) No
4 \(\dfrac{e^x}{ex^e}\) No

Our calculated derivative matches Option 1.

Revision Table: Key Differentiation Formulas

Here are some fundamental differentiation formulas used in calculus:

Function \(f(x)\) Derivative \(f'(x) = \frac{d}{dx}(f(x))\)
\(c\) (constant) \(0\)
\(x^n\) \(nx^{n-1}\)
\(e^x\) \(e^x\)
\(a^x\) \(a^x \ln a\)
\(\ln x\) \(\frac{1}{x}\)
\(\log_a x\) \(\frac{1}{x \ln a}\)

Additional Information: Differentiation Techniques

Understanding different differentiation techniques is crucial for solving calculus problems. Here are a few related concepts:

  • Chain Rule: Used to find the derivative of a composite function. If \(y = f(g(x))\), then \(\frac{dy}{dx} = f'(g(x)) \cdot g'(x)\). The method used in the problem, \(\frac{dy}{du} = \frac{dy/dx}{du/dx}\), is a direct consequence of the chain rule where \(y\) is a function of \(u\), and \(u\) is a function of \(x\). If \(y = F(u)\) and \(u = g(x)\), then \(y = F(g(x))\). By the chain rule, \(\frac{dy}{dx} = F'(g(x)) \cdot g'(x) = \frac{dF}{du} \cdot \frac{du}{dx}\). Rearranging gives \(\frac{dF}{du} = \frac{dy/dx}{du/dx}\), which is \(\frac{dy}{du} = \frac{dy/dx}{du/dx}\).
  • Product Rule: Used to find the derivative of a product of two functions. If \(h(x) = f(x)g(x)\), then \(h'(x) = f'(x)g(x) + f(x)g'(x)\).
  • Quotient Rule: Used to find the derivative of a quotient of two functions. If \(h(x) = \frac{f(x)}{g(x)}\), then \(h'(x) = \frac{f'(x)g(x) - f(x)g'(x)}{(g(x))^2}\).
  • Implicit Differentiation: Used to find the derivative of a function defined implicitly by an equation, where \(y\) is not explicitly expressed as a function of \(x\).

Mastering these techniques and fundamental formulas is essential for tackling various differentiation problems in calculus.

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