Math Problem Statement

You have been asked to design a rectangular box with a square base and an open top. The volume of the box must be 24cm3 . Determine the minimum surface area necessary to construct a box of this volume. Enter an exact answer.

Solution

We are asked to find the minimum surface area necessary to construct a rectangular box with a square base and an open top, where the volume is 24 cm³. Let’s define the variables:

  • Let xx be the side length of the square base (in cm).
  • Let hh be the height of the box (in cm).
  • The volume of the box is given as V=x2h=24cm3V = x^2 h = 24 \, \text{cm}^3.

Step 1: Express hh in terms of xx

From the volume equation x2h=24x^2 h = 24, we can solve for hh: h=24x2h = \frac{24}{x^2}

Step 2: Express the surface area in terms of xx

The surface area of the box consists of:

  • The area of the square base: x2x^2,
  • The area of the four sides (each side has an area of x×hx \times h).

The total surface area SS is: S=x2+4(xh)S = x^2 + 4(x \cdot h) Substitute h=24x2h = \frac{24}{x^2} into this equation: S=x2+4(x24x2)S = x^2 + 4 \left( x \cdot \frac{24}{x^2} \right) Simplify: S=x2+96xS = x^2 + \frac{96}{x}

Step 3: Minimize the surface area

To find the value of xx that minimizes the surface area, we first take the derivative of SS with respect to xx and set it equal to zero.

dSdx=2x96x2\frac{dS}{dx} = 2x - \frac{96}{x^2} Set the derivative equal to zero: 2x96x2=02x - \frac{96}{x^2} = 0 Multiply through by x2x^2 to eliminate the fraction: 2x3=962x^3 = 96 Solve for xx: x3=48x^3 = 48 x=483x = \sqrt[3]{48} This simplifies to: x=263x = 2\sqrt[3]{6}

Step 4: Find the corresponding height hh

Now that we know x=263x = 2\sqrt[3]{6}, substitute it into the volume equation to find hh: [ h = \frac{24}{x^2} = \frac{24}{\left(2\sqrt[3]{6}\right)^2} = \frac{24}{4 \cdot \sqrt[3]{36}} ]

Step 5: Calculate the minimum surface area

To finalize, substitute x=263x = 2\sqrt[3]{6} into the surface area formula S=x2+96xS = x^2 + \frac{96}{x}.

This results in an

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Math Problem Analysis

Mathematical Concepts

Calculus
Optimization
Geometry

Formulas

Volume of a box with a square base: V = x^2 * h
Surface area of a box with a square base and open top: S = x^2 + 4xh
Derivative of surface area: dS/dx = 2x - 96/x^2

Theorems

Optimization using the derivative
Critical points of a function

Suitable Grade Level

Grade 11-12 or Early College