General Formula for the Reciprocal of a Sum of Reciprocals

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The discussion centers on finding a general formula for the reciprocal of a sum of reciprocals, specifically expressed as 1/(1/x1 + 1/x2 + ... + 1/xn). The reduced mass formula is referenced as a related concept, illustrating the relationship between individual masses and their combined effect. A proposed expression for the reciprocal sum is presented, involving products of the variables and their sums. The conversation emphasizes the mathematical equivalence of different formulations for clarity. Overall, the thread seeks to establish a clear and simplified method for calculating this type of reciprocal sum.
FredericChopin
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I know that the reduced mass, μ, of an object is:

\mu = \frac{1}{\frac{1}{m_1} + \frac{1}{m_2}}

\mu = \frac{m_1 m_2}{ m_1 + m_2 }

But is there a general formula (or a simplified expression) for finding the value of:

\frac{1}{ \frac{1}{x_1} + \frac{1}{x_2} + ... + \frac{1}{x_n} } ?

Thank you.
 
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This is the same as solving:
\dfrac{1}{x1}+\dfrac{1}{x2}+\dfrac{1}{x3}+... = \dfrac{A}{B}

\left( \dfrac{1}{x1}+\dfrac{1}{x2}+\dfrac{1}{x3}+... \right)^{-1}= \dfrac{\prod_1 x_i}{\sum_i \prod_{j\neq i} x_j}
 
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matteo137 said:
This is the same as solving:
\dfrac{1}{x1}+\dfrac{1}{x2}+\dfrac{1}{x3}+... = \dfrac{A}{B}

\left( \dfrac{1}{x1}+\dfrac{1}{x2}+\dfrac{1}{x3}+... \right)^{-1}= \dfrac{\prod_1 x_i}{\sum_i \prod_{j\neq i} x_j}

Great! Thank you so much!
 
Here is a little puzzle from the book 100 Geometric Games by Pierre Berloquin. The side of a small square is one meter long and the side of a larger square one and a half meters long. One vertex of the large square is at the center of the small square. The side of the large square cuts two sides of the small square into one- third parts and two-thirds parts. What is the area where the squares overlap?

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