What is the Maximum Product of Two Numbers that Sum to 120?

  • Thread starter whitehorsey
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Thank you!In summary, to find two numbers whose sum is 120 and whose product is a maximum, you can express the product as a function of one variable by substituting one variable in terms of the other. This creates a parabola, and the vertex of the parabola will give you the maximum product. This can also be done using calculus by finding the derivative of the function and setting it to 0 to find the maximum value. Another method is to graph the function and find the vertex.
  • #1
whitehorsey
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1. Find two numbers x and y whose sum is 120 and whose product is a maximum.



2. none



3. x + y = 120
xy = maximum
x = 120 - y
I wrote these down but I don't know what to do next. Can you please show me? :) Thank You!
 
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  • #2
Well you have the function P = xy which you want to maximize, however it contains two variables. Are they independent though? How can you reduce this function down to a single variable function?
 
  • #3
whitehorsey said:
1. Find two numbers x and y whose sum is 120 and whose product is a maximum.



2. none



3. x + y = 120
xy = maximum
x = 120 - y
I wrote these down but I don't know what to do next. Can you please show me? :) Thank You!
Replace the x in xy with 120- y so you have only one variable. Now, do you know how to "apply the derivative" to find where a function has a maximum or minimum?
 
  • #4
As an alternate approach, the graph of your area function, as a function of either x or y alone, is a parabola. You can find the vertex of the parabola, at which the maximum area is attained, without using calculus.
 
  • #5
Ah! Excellent point.
 

Related to What is the Maximum Product of Two Numbers that Sum to 120?

1. What is the purpose of applying the derivative?

The derivative measures the rate of change of a function at a specific point, which can be useful in various applications such as optimization, finding critical points, and understanding the behavior of a function.

2. How do you apply the derivative to a function?

The derivative of a function can be found by using the rules of differentiation, such as the power rule, product rule, chain rule, and quotient rule. These rules allow us to find the derivative of a function at any given point.

3. Can the derivative be used to find the maximum or minimum value of a function?

Yes, the derivative can be used to find the critical points of a function, where the derivative is equal to zero or undefined. These points can correspond to maximum or minimum values of the function.

4. What is the relationship between the derivative and the slope of a tangent line?

The derivative of a function at a specific point is equal to the slope of the tangent line at that point. This means that the derivative can be used to find the slope of a tangent line to a curve at any given point.

5. Are there any real-world applications of applying the derivative?

Yes, there are many real-world applications of the derivative. For example, it can be used in economics to maximize profits, in physics to analyze motion and acceleration, and in biology to study growth and rates of change in populations.

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