Numbers Finder by Product and Sum of Squares

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Calculate Two Numbers Using Their Product and Sum of Squares

Result

How to Calculate Two Numbers Using Their Product and Sum of Squares

Given:

  • \( P \): the product of the two numbers (\( x \cdot y \))
  • \( S \): the sum of their squares (\( x^2 + y^2 \))

Steps:

  1. Set up relationships: \( x \cdot y = P, \quad x^2 + y^2 = S \)
  2. Use the expanded sum of squares formula: \( (x + y)^2 = x^2 + y^2 + 2xy \) Substituting \( S \) and \( P \): \( (x + y)^2 = S + 2P \)
  3. Solve for \( x + y \): \( x + y = \sqrt{S + 2P} \)
  4. Form a quadratic equation for \( x \) and \( y \) based on sum and product: \( t^2 - (x + y)t + xy = 0 \)
  5. Solve the quadratic equation: \( x, y = \frac{S \pm \sqrt{S^2 - 4 \cdot P}}{2} \)

Examples

Example 1: The product of two numbers is 40, and their sum of squares is 404. What are the numbers?

Solution:

1. Calculate \( x + y \):

\( x + y = \sqrt{404 + 2 \cdot 40} = \sqrt{484} = 22 \)

2. Form the quadratic equation:

\( t^2 - 22t + 40 = 0 \)

3. Calculate the discriminant:

\( \sqrt{22^2 - 4 \cdot 40} = \sqrt{484 - 160} = \sqrt{324} = 18 \)

4. Solve for \( t \):

\( t = \frac{22 \pm 18}{2} \implies t = 20 \text{ or } 2 \)

Result: The numbers are 20 and 2.

Example 2: The product of two numbers is 120, and their sum of squares is 289. What are the numbers?

Solution:

1. Calculate \( x + y \):

\( x + y = \sqrt{289 + 2 \cdot 120} = \sqrt{529} = 23 \)

2. Form the quadratic equation:

\( t^2 - 23t + 120 = 0 \)

3. Calculate the discriminant:

\( \sqrt{23^2 - 4 \cdot 120} = \sqrt{529 - 480} = \sqrt{49} = 7 \)

4. Solve for \( t \):

\( t = \frac{23 \pm 7}{2} \implies t = 15 \text{ or } 8 \)

Result: The numbers are 15 and 8.

Example 3: The product of two numbers is 108, and their sum of squares is 225. What are the numbers?

Solution:

1. Calculate \( x + y \):

\( x + y = \sqrt{225 + 2 \cdot 108} = \sqrt{441} = 21 \)

2. Form the quadratic equation:

\( t^2 - 21t + 108 = 0 \)

3. Calculate the discriminant:

\( \sqrt{21^2 - 4 \cdot 108} = \sqrt{441 - 432} = \sqrt{9} = 3 \)

4. Solve for \( t \):

\( t = \frac{21 \pm 3}{2} \implies t = 12 \text{ or } 9 \)

Result: The numbers are 12 and 9.