LeGrange multiplier with inequality

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In summary, the problem is to find the dimensions of the box with the largest volume under the constraint that the perimeter of the cross section perpendicular to the length is at most 108. The equation for volume is given as f(x,y,z)=xyz and the constraint is 2x+2z<108. The solver attempted to use a Lagrange multiplier to find the maximum volume, but determined that the volume has no maximum since y can be taken as large as desired regardless of the values of x and z. It is suggested to re-read the problem as it may state a different constraint such as the sum of the length of the box and its perimeter being bounded.
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memish
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Homework Statement


Find the dimensions of the box with the largest volume, given the constraint that the perimeter of the cross sector perpendicular to length is at msot 108


Homework Equations


So I have f(x,y,z)=xyz
and the constraint is 2x+2z<108


The Attempt at a Solution


I set up the legrange multipler <yz, xz, xy>=(multiplier)<2, 0, 2>
So then you have
yz=2(multiplier)
yx=2(multiplier)
xz=0(multiplier)
and then 2x+2z<108
But since xz=0(m), I can't figure out how to solve the 4 equations to get the possible points. If I have xz=0, then either x or z is 0, right? but then there would be no volume..any ideas? Thanks!
 
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  • #2
You probably have the problem stated incorrectly. As stated, the volume has no max because you could take y as large as you want no matter what x and z are.

Re-read the problem. My guess is that it will say something like "the length of the box plus the perimeter" is bounded.
 

FAQ: LeGrange multiplier with inequality

1. What is the LeGrange multiplier with inequality?

The LeGrange multiplier with inequality is a mathematical method used to optimize a function subject to one or more constraints. It is an extension of the LeGrange multiplier method, which is used for optimizing functions with equality constraints.

2. How does the LeGrange multiplier with inequality work?

The LeGrange multiplier with inequality works by introducing a new variable, called the multiplier, to the original function. The multiplier is then used to adjust the original function in such a way that it satisfies the constraints imposed by the inequality. This results in a new function that can be optimized using traditional methods.

3. When is the LeGrange multiplier with inequality used?

The LeGrange multiplier with inequality is used when optimizing a function with one or more inequality constraints. It is commonly used in economics, finance, and engineering to solve optimization problems that involve constraints, such as limited resources or budget constraints.

4. What are the key benefits of using the LeGrange multiplier with inequality?

One of the main benefits of using the LeGrange multiplier with inequality is that it allows for the optimization of functions with constraints, which is not possible using traditional methods. It also provides a systematic approach to solving optimization problems with constraints and can handle multiple constraints simultaneously.

5. Are there any limitations to the LeGrange multiplier with inequality?

One limitation of the LeGrange multiplier with inequality is that it only works for differentiable functions. It also requires the constraints to be convex, which means they cannot have any concave points. Additionally, the method may become computationally intensive for complex functions with multiple constraints.

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