Math Problem Statement

At what point does the curve have maximum curvature? y = 5 ln(x) (xy) =

Solution

To find the point of maximum curvature for the function y=5ln(x)y = 5 \ln(x), we need to calculate the curvature κ\kappa of the curve and find where it is maximized.

The curvature κ\kappa of a curve defined by y=f(x)y = f(x) is given by:

κ=f(x)(1+(f(x))2)3/2\kappa = \frac{|f''(x)|}{(1 + (f'(x))^2)^{3/2}}

Step 1: First and Second Derivatives

For y=5ln(x)y = 5 \ln(x), we need to find f(x)f'(x) and f(x)f''(x):

  1. First derivative: f(x)=ddx(5ln(x))=5xf'(x) = \frac{d}{dx}(5 \ln(x)) = \frac{5}{x}

  2. Second derivative: f(x)=ddx(5x)=5x2f''(x) = \frac{d}{dx}\left(\frac{5}{x}\right) = -\frac{5}{x^2}

Step 2: Curvature Formula

Substitute f(x)f'(x) and f(x)f''(x) into the curvature formula:

κ=5x2(1+(5x)2)3/2=5x2(1+25x2)3/2\kappa = \frac{\left| -\frac{5}{x^2} \right|}{\left(1 + \left(\frac{5}{x}\right)^2\right)^{3/2}} = \frac{\frac{5}{x^2}}{\left(1 + \frac{25}{x^2}\right)^{3/2}}

Step 3: Simplify the Expression

To make this easier to analyze, let’s simplify the denominator:

κ=5/x2(1+25/x2)3/2\kappa = \frac{5/x^2}{(1 + 25/x^2)^{3/2}}

Rewrite 1+25x21 + \frac{25}{x^2} with a common denominator:

1+25x2=x2+25x21 + \frac{25}{x^2} = \frac{x^2 + 25}{x^2}

Thus, we have:

κ=5/x2(x2+25x2)3/2=5x2x3(x2+25)3/2\kappa = \frac{5/x^2}{\left(\frac{x^2 + 25}{x^2}\right)^{3/2}} = \frac{5}{x^2} \cdot \frac{x^3}{(x^2 + 25)^{3/2}}

This simplifies to:

κ=5x(x2+25)3/2\kappa = \frac{5x}{(x^2 + 25)^{3/2}}

Step 4: Maximize the Curvature

To find the point of maximum curvature, differentiate κ\kappa with respect to xx and set the derivative equal to zero. Solving this can be complex, so let's proceed by finding critical points or testing values for xx to locate the maximum.

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Math Problem Analysis

Mathematical Concepts

Calculus
Curvature
Derivatives
Maximization

Formulas

Curvature formula: κ = |f''(x)| / (1 + (f'(x))^2)^(3/2)
First derivative: f'(x) = 5/x
Second derivative: f''(x) = -5/x^2

Theorems

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Suitable Grade Level

Undergraduate Calculus