Math Problem Statement

A piece of wire 16 m long is cut into two pieces. One piece is bent into a square and the other into an equilateral triangle. (a) How much wire should be used for the square to maximize the total area? (b) How much wire should be used for the square to minimize the total area?

Solution

To solve the problem, let’s break it down:

Definitions:

  1. A wire of 16 m is divided into two pieces.
  2. One piece is bent into a square, and the other into an equilateral triangle.
  3. Let x be the length of the wire used for the square, and 16 - x be the length used for the triangle.

Formulas:

  • Square Area: If the perimeter of the square is xx, the side length is x4\frac{x}{4}, and the area is: Asquare=(x4)2=x216.A_{\text{square}} = \left(\frac{x}{4}\right)^2 = \frac{x^2}{16}.

  • Equilateral Triangle Area: If the perimeter of the triangle is 16x16 - x, each side is 16x3\frac{16 - x}{3}, and the area is: Atriangle=34(16x3)2=336(16x)2.A_{\text{triangle}} = \frac{\sqrt{3}}{4} \left(\frac{16 - x}{3}\right)^2 = \frac{\sqrt{3}}{36} (16 - x)^2.

  • Total Area: The total area AA is the sum of the two: A(x)=x216+336(16x)2.A(x) = \frac{x^2}{16} + \frac{\sqrt{3}}{36} (16 - x)^2.

Steps to Solve:

(a) Maximize Total Area:

We need to find xx that maximizes A(x)A(x). To do this:

  1. Compute the derivative A(x)A'(x).
  2. Solve A(x)=0A'(x) = 0 to find critical points.
  3. Use the second derivative test or boundary values (x=0x = 0 or x=16x = 16) to confirm the maximum.

(b) Minimize Total Area:

To minimize A(x)A(x), follow the same steps as above but identify the xx corresponding to the minimum.

Let me calculate these values for you. sympy as sp

Define variables

x = sp.symbols('x') total_length = 16

Area formulas

A_square = (x**2) / 16 # Square area A_triangle = (sp.sqrt(3) / 36) * (total_length - x)**2 # Triangle area A_total = A_square + A_triangle # Total area

Derivative of the total area

A_prime = sp.diff(A_total, x)

Solve critical points

critical_points = sp.solve(A_prime, x)

Evaluate second derivative to classify critical points

A_double_prime = sp.diff(A_prime, x) critical_values = [(cp, A_total.subs(x, cp), A_double_prime.subs(x, cp)) for cp in critical_points]

Boundary points for total area

boundary_values = [(0, A_total.subs(x, 0)), (total_length, A_total.subs(x, total_length))]

critical_values, boundary_valuesThe critical points and boundary values have been analyzed. Here's the result:

  1. Critical point: x=25611+192311x = -\frac{256}{11} + \frac{192\sqrt{3}}{11} meters for the square.
    • Corresponding total area: (25611+192311)216+336(16(25611+192311))2\frac{(-\frac{256}{11} + \frac{192\sqrt{3}}{11})^2}{16} + \frac{\sqrt{3}}{36} (16 - (-\frac{256}{11} + \frac{192\sqrt{3}}{11}))^2.
    • Nature (from second derivative): Positive, indicating **minimize area}.

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Math Problem Analysis

Mathematical Concepts

Optimization
Quadratic Functions
Geometry

Formulas

Area of a square = (side length)^2
Area of an equilateral triangle = (sqrt(3)/4) * (side length)^2

Theorems

First Derivative Test
Second Derivative Test

Suitable Grade Level

Grades 11-12