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Find two positive real numbers whose sum is 26 and product is maximum.
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This pair of two positive real numbers is (13,13).
For any other pair of real numbers with the sum of 26,  these numbers are of the form  (13+x,13-x),
and their product  (13+x)*(13-x) = 169-x^2  is LESS THAN 13*13= 169.
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