If y = √(x / √(x / √(x / √...))) (infinite nested radical), then the value of dy/dx at x = 8 is:
Step-by-Step Solution
Key Concept: Infinite nested radical simplification, power rule differentiation
Step 1: Recognize the self-similar structure of the infinite nested radical.
Since the expression $y = \sqrt{\frac{x}{\sqrt{\frac{x}{\sqrt{\frac{x}{\sqrt{\cdots}}}}}}}$ is infinite and self-similar, the denominator inside the first square root is also equal to $y$. Therefore, we can write:
$$y = \sqrt{\frac{x}{y}}$$
Step 2: Eliminate the square root by squaring both sides.
Squaring both sides of the equation:
$$y^2 = \frac{x}{y}$$
Multiplying both sides by $y$:
$$y^3 = x$$
Step 3: Express $y$ as a power function of $x$.
From the relation $y^3 = x$, we can solve for $y$:
$$y = x^{1/3}$$
Step 4: Differentiate with respect to $x$.
Using the power rule for differentiation:
$$\frac{dy}{dx} = \frac{1}{3}x^{-2/3} = \frac{1}{3x^{2/3}}$$
Step 5: Evaluate the derivative at $x = 8$.
Substituting $x = 8$:
$$\frac{dy}{dx}\bigg|_{x=8} = \frac{1}{3}(8)^{-2/3}$$
Since $8 = 2^3$, we have $(8)^{-2/3} = (2^3)^{-2/3} = 2^{-2} = \frac{1}{4}$
Therefore:
$$\frac{dy}{dx}\bigg|_{x=8} = \frac{1}{3} \cdot \frac{1}{4} = \frac{1}{12}$$
**Final Answer:** The value of $\frac{dy}{dx}$ at $x = 8$ is $\boxed{\frac{1}{12}}$, which corresponds to **Option 2**.
Correct Answer: 2