The product of two positive numbers is 16. Determine these two numbers is that the square of one plus the cube of the other is the smallest.

We are tasked with finding two positive numbers whose product is 16, and such that the square of one number plus the cube of the other is minimized.

Let the two positive numbers be \( x \) and \( y \), such that:
\[
x \cdot y = 16
\]
We want to minimize the function:
\[
f(x, y) = x^2 + y^3
\]
To simplify the problem, we can express \( y \) in terms of \( x \) using the product constraint \( x \cdot y = 16 \), which gives:
\[
y = \frac{16}{x}
\]
Now substitute this into the function to minimize:
\[
f(x) = x^2 + \left(\frac{16}{x}\right)^3 = x^2 + \frac{4096}{x^3}
\]
Next, we find the critical points by differentiating \( f(x) \) with respect to \( x \) and setting the derivative equal to zero. First, compute the derivative:
\[
f'(x) = 2x - 3 \cdot \frac{4096}{x^4}
\]
Set \( f'(x) = 0 \) to find critical points:
\[
2x = \frac{12288}{x^4}
\]
Multiply both sides by \( x^4 \) to clear the fraction:
\[
2x^5 = 12288
\]
Solve for \( x \):
\[
x^5 = 6144
\]
\[
x = \sqrt[5]{6144}
\]
Using the approximation \( \sqrt[5]{6144} \approx 5.2 \).

Now, substitute \( x = 5.2 \) into \( y = \frac{16}{x} \) to find \( y \):
\[
y = \frac{16}{5.2} \approx 3.08
\]

Thus, the two numbers are approximately \( x = 5.2 \) and \( y = 3.08 \).

Would you like more details on any part of this solution?

---

Here are 5 questions that relate to this problem:
1. What would happen if the product constraint was different from 16?
2. How do we find critical points using derivatives?
3. What is the significance of minimizing the sum of squares and cubes in this context?
4. Could this problem be solved using Lagrange multipliers?
5. How does the approximation of \( \sqrt[5]{6144} \) affect the accuracy of the result?

**Tip:** When minimizing or maximizing a function, always check the second derivative to confirm if the critical point is a minimum or maximum.

The product of two positive numbers is 16. Determine these two numbers such that the square of one plus the cube of the other is the smallest.

This problem explores the optimization of two numbers whose product is 16, by minimizing the sum of the square of one and the cube of the other. Key algebraic and calculus concepts such as derivatives and critical points are used to find the solution. Suitable for students in Grades 10-12.

Math Problem Statement

Solution

Ask a new question for Free

By Image

Math Problem Analysis

Mathematical Concepts

Formulas

Theorems

Suitable Grade Level

Related Recommendation