if {x(adsbygoogle = window.adsbygoogle || []).push({}); _{1}, x_{2}, .....x_{i}} and {y_{1},y_{2},.....y_{i}} are finite sets.

are two sets of real numbers. Then sum

Ʃ x_{i}x_{j }+y_{i}y_{j}must be maximum, and i≠j

so is there some general condition to solve this problem?

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# Simple Arithmetic Question

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