Numbers Finder by Sum of Squares and Square of Sum

Input the sum of squares and the square of the sum to quickly find two numbers!

Calculate Two Numbers Using the Sum of Squares and the Square of Sum

Result

How to Calculate Two Numbers Using the Sum of Squares and the Square of Sum

Let \(x\) and \(y\) be the two numbers. Suppose their sum of squares (\(S\)) and square of the sum (\(T\)) are given.

  1. Formulas to start with: Sum of squares: \( x^2 + y^2 = S\) Square of the sum: \((x + y)^2 = T\)
  2. Expand the square of the sum formula: \( (x + y)^2 = x^2 + y^2 + 2xy\) Substituting the known values: \( T = S + 2xy\)
  3. Solve for \(xy\): \( xy = \frac{T - S}{2}\)
  4. Using the sum and product of roots formula, the quadratic equation becomes: \( t^2 - (x + y)t + xy = 0\)
  5. Substituting \(x + y = \sqrt{T}\) and \(xy = \frac{T - S}{2}\), the equation is: \( t^2 - \sqrt{T}t + \frac{T - S}{2} = 0\)
  6. Solve for \(x\) and \(y\): \( t = \frac{\sqrt{T} \pm \sqrt{T - 2S}}{2}\) The solutions for \(x\) and \(y\) are obtained.

Examples

Example 1: The sum of squares is 225, and the square of the sum is 441. Find the two numbers.

Solution:

1. Compute \(x + y\):

\( x + y = \sqrt{T} = \sqrt{441} = 21\)

2. Compute \(xy\):

\( xy = \frac{T - S}{2} = \frac{441 - 225}{2} = \frac{216}{2} = 108\)

3. Form the quadratic equation:

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

4. Solve for \(x\) and \(y\):

\( t = \frac{21 \pm \sqrt{21^2 - 4 \times 108}}{2} = \frac{21 \pm \sqrt{441 - 432}}{2} = \frac{21 \pm 3}{2}\)

\(x = 12\) and \(y = 9\)

Result: The two numbers are 12 and 9.

Example 2: The sum of squares is 100, and the square of the sum is 196. Find the two numbers.

Solution:

1. Compute \(x + y\):

\( x + y = \sqrt{T} = \sqrt{196} = 14\)

2. Compute \(xy\):

\( xy = \frac{T - S}{2} = \frac{196 - 100}{2} = \frac{96}{2} = 48\)

3. Form the quadratic equation:

\( t^2 - 14t + 48 = 0\)

4. Solve for \(x\) and \(y\):

\( t = \frac{14 \pm \sqrt{14^2 - 4 \times 48}}{2} = \frac{14 \pm \sqrt{196 - 192}}{2} = \frac{14 \pm 2}{2}\)

\(x = 8\) and \(y = 6\).

Result: The two numbers are 8 and 6.

Example 3: The sum of squares is 313, and the square of the sum is 625. Find the two numbers.

Solution:

1. Compute \(x + y\):

\( x + y = \sqrt{T} = \sqrt{625} = 25\)

2. Compute \(xy\):

\( xy = \frac{T - S}{2} = \frac{625 - 313}{2} = \frac{312}{2} = 156\)

3. Form the quadratic equation:

\( t^2 - 25t + 156 = 0\)

4. Solve for \(x\) and \(y\):

\( t = \frac{25 \pm \sqrt{25^2 - 4 \times 156}}{2} = \frac{25 \pm \sqrt{625 - 624}}{2} = \frac{25 \pm 1}{2}\)

\(x = 13\) and \(y = 12\).

Result: The two numbers are 13 and 12.