e = one diagonal
f = the other diagonal
h ist the height of the rhombus
\(\boxed{~ \begin{array}{rcll} h &=&\frac{ e\cdot f }{\sqrt{ e^2 + f^2 }} \\ \end{array} ~}\\\)
or
\(\begin{array}{rcll} h &=&\frac{ e\cdot f }{\sqrt{ e^2 + f^2 }}\\ h &=&\frac{ 1 }{ \frac { \sqrt{ e^2 + f^2 }}{ e\cdot f}} \\ h &=&\frac{ 1 }{ \sqrt{ \frac{e^2}{e^2\cdot f^2} + \frac{f^2}{e^2\cdot f^2} }} \\ h &=&\frac{ 1 }{ \sqrt{ \frac{1}{f^2} + \frac{1}{e^2} }} \\ \frac{1}{h} &=&\sqrt{ \frac{1}{f^2} + \frac{1}{e^2} } \\ \frac{1}{h^2} &=&\frac{1}{f^2} + \frac{1}{e^2} \\ \frac{1}{h^2} &=&\frac{1}{e^2} + \frac{1}{f^2} \\ \end{array}\)
\(\boxed{~ \begin{array}{rcll} \frac{1}{h^2} &=&\frac{1}{e^2} + \frac{1}{f^2} \end{array} ~}\)

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