Math Problem Statement

Use differentiation to find the value of x that minimises, 2x^2 + 64/x

Solution

To find the value of xx that minimizes the function f(x)=2x2+64xf(x) = 2x^2 + \frac{64}{x}, we will use differentiation. Here are the steps:

1. Differentiate the function:

First, let's find the first derivative of f(x)f(x) with respect to xx.

f(x)=2x2+64xf(x) = 2x^2 + \frac{64}{x}

The first derivative, f(x)f'(x), is calculated as:

f(x)=ddx(2x2)+ddx(64x)f'(x) = \frac{d}{dx} \left( 2x^2 \right) + \frac{d}{dx} \left( \frac{64}{x} \right)

f(x)=4x64x2f'(x) = 4x - \frac{64}{x^2}

2. Set the first derivative equal to zero:

To find the critical points, set f(x)=0f'(x) = 0 and solve for xx.

4x64x2=04x - \frac{64}{x^2} = 0

3. Solve for xx:

Multiply both sides of the equation by x2x^2 to eliminate the fraction:

4x364=04x^3 - 64 = 0

4x3=644x^3 = 64

x3=16x^3 = 16

x=163x = \sqrt[3]{16}

The value of xx that minimizes the function is x=163x = \sqrt[3]{16}.

4. Confirm that this is a minimum:

To confirm that this critical point is a minimum, we can check the second derivative, f(x)f''(x).

f(x)=ddx(4x64x2)f''(x) = \frac{d}{dx} \left( 4x - \frac{64}{x^2} \right)

f(x)=4+128x3f''(x) = 4 + \frac{128}{x^3}

Since f(x)>0f''(x) > 0 for all x>0x > 0, the function is concave up at x=163x = \sqrt[3]{16}, confirming that this is indeed a minimum.

Thus, the value of xx that minimizes the function is x=163x = \sqrt[3]{16}.

Would you like details or have any questions about the process?


Here are 5 related questions for further exploration:

  1. How would the minimum value change if the function were 3x2+64x3x^2 + \frac{64}{x}?
  2. What happens to the minimum value if f(x)=2x2+64x+10f(x) = 2x^2 + \frac{64}{x} + 10?
  3. How do you find the maximum value of a function using differentiation?
  4. What is the significance of the second derivative in determining the nature of a critical point?
  5. Can you apply this method to find the minimum of a more complex function, such as 2x2+64x+x42x^2 + \frac{64}{x} + x^4?

Tip: Always verify if a critical point is a minimum or maximum by checking the second derivative or using the first derivative test.

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Math Problem Analysis

Mathematical Concepts

Differentiation
Critical Points
Optimization

Formulas

First derivative of a function f'(x)
Second derivative of a function f''(x)

Theorems

First Derivative Test
Second Derivative Test

Suitable Grade Level

Grades 11-12