Algebra Level 3

$\frac{x^2}{10}+\frac{28}{x}=\frac{7x}{5}-\frac{40}{x^2}$

The equation above has 4 real roots $x_1$, $x_2$, $x_3$, and $x_4$ such that $x_1. Find the value of $x_1x_3+x_2x_4$.

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