Numbers Finder Using Geometric and Harmonic Means

Input the geometric mean and harmonic mean of two numbers to instantly find their values.

Calculate Two Numbers Using Geometric and Harmonic Means

Result

How to Calculate Numbers Using Geometric and Harmonic Means

Let the two numbers be \(x\) and \(y\). You are given their geometric mean (\(G\)) and harmonic mean (\(H\)).

Definitions of Geometric and Harmonic Means

Geometric Mean (G): The square root of the product of the two numbers: \( G = \sqrt{x \cdot y} \)

Harmonic Mean (H): The reciprocal of the average of the reciprocals of the two numbers: \( H = \frac{2xy}{x + y} \)

Deriving the Formula

Using the geometric mean, calculate the product of the two numbers: \( x \cdot y = G^2 \) Substitute the product into the harmonic mean formula to find the sum of the two numbers: \( x + y = \frac{2xy}{H} \) \( x + y = \frac{2G^2}{H} \) Using the sum and product, construct a quadratic equation: \( t^2 - \frac{2G^2}{H}t + G^2 = 0 \) Apply the quadratic formula to find \(t\): \( t = \frac{ \frac{2G^2}{H} \pm \sqrt{( \frac{2G^2}{H})^2 - 4 \cdot G^2}}{2} \) The two solutions correspond to \(x\) and \(y\).

Examples

Example 1: Find two numbers whose geometric mean is 12 and harmonic mean is 7.2

Solution:

1. Calculate the Product \( x \cdot y \):

\( x \cdot y = 12^2 = 144 \)

2. Calculate the Sum \( x + y \):

\( x + y = \frac{2 \cdot 12^2}{7.2} = \frac{2 \cdot 144}{7.2} = 40 \)

3. Form the Quadratic Equation:

\( t^2 - 40t + 144 = 0 \)

4. Solve the Equation:

\( t = \frac{40 \pm \sqrt{40^2 - 4 \cdot 144}}{2} = \frac{40 \pm \sqrt{1600 - 576}}{2} = \frac{40 \pm \sqrt{1024}}{2} \)

\( t_1 = \frac{40 + \sqrt{1024}}{2} = 36 \)

\( t_2 = \frac{40 - \sqrt{1024}}{2} = 4 \)

Result: The two numbers are 36 and 4.

Example 2: The geometric mean of two numbers is 6 and their harmonic mean is \( \frac{72}{13} \), find the two number.

Solution:

1. Calculate the Product \( x \cdot y \):

\( x \cdot y = 6^2 = 36 \)

2. Calculate the Sum \( x + y \):

\( x + y = \frac{2 \cdot 6^2}{\frac{72}{13}} = \frac{2 \cdot 36}{\frac{72}{13}} = \frac{72 \cdot 13}{72} = 13 \)

3. Form the Quadratic Equation:

\( t^2 - 13t + 36 = 0 \)

4. Solve the Equation:

\( t = \frac{13 \pm \sqrt{13^2 - 4 \cdot 36}}{2} = \frac{13 \pm \sqrt{169 - 144}}{2} = \frac{13 \pm \sqrt{25}}{2} \)

\( t_1 = \frac{13 + \sqrt{25}}{2} = 9 \)

\( t_2 = \frac{13 - \sqrt{25}}{2} = 4 \)

Result: The two numbers are 9 and 4.