How Should Wire Be Cut to Minimize Combined Area of Circle and Square?

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SUMMARY

The problem involves cutting a 10ft wire into two pieces, one forming a circle and the other a square, to minimize the combined area of both shapes. The optimal dimensions are derived as radius r = 5/(π + 4) for the circle and side length s = 10/(π + 4) for the square. The solution requires establishing the relationship between the wire lengths and the areas of the shapes, leading to the formulation of a total area function A(a, b) = A1(a) + A2(b). Differentiating this function and setting it to zero yields the minimum area configuration.

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  • Understanding of basic geometry, specifically the formulas for the area of a circle and a square.
  • Knowledge of calculus, particularly differentiation and optimization techniques.
  • Familiarity with algebraic manipulation to establish relationships between variables.
  • Ability to apply the method of Lagrange multipliers for constrained optimization (optional but beneficial).
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  • Study the formulas for the area of a circle (A = πr²) and a square (A = s²).
  • Learn about optimization techniques in calculus, focusing on finding critical points of functions.
  • Explore the method of Lagrange multipliers for solving constrained optimization problems.
  • Practice similar optimization problems involving geometric shapes and constraints.
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Homework Statement



A piece of wire 10ft long is cut into two pieces. One piece is bent into the shape of a circle and the other into the shape of a square. How should the wire be cut so that the combined area of the two figures is as small as possible

Homework Equations


The Attempt at a Solution


radius=r and side of the square=s
answer: r = 5/(pi+4) and s =10/(pi+4)

I have the answer but I don't know how should I do it... Please help
 
Last edited:
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A piece of wire 10ft long is cut into two pieces. One piece is bent ito the shape of a circle and the other into the shape of a square. How should the wire be cut so that the combined area of the two figures is as small as possible

should that be
A piece of wire 10ft long is to be cut into two pieces. One piece is bent ito the shape of a circle and the other into the shape of a square. How should the wire be cut so that the combined area of the two figures is as small as possible
 
Write down the equations for the area of a circle and the area of a square. The area of the circle has the parameter r (the radius) and the area of the square has the parameter s (the side of the square). Find the connection between these parameters and between the parameters a and b which represent the two cut pieces of the wire. Further on, create a sum A(a, b) = A1(a) + A2(b). Then plug in the relation between a and b (i.e. a + b = 10). Then you'll get the total area in a single variable, A(a) = ... (or A(b), doesn't matter). Differentiate with respect to that variable and set equal to zero.
 

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