SOLUTION: Among all pairs of numbers whose sum is 16.8, find a pair whose product is as large as possible. What is the maximum​ product?

For x + u = N, the maximum product xy is 



So   will be the max product.



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Derivation:

x + y = N --->  y = N-x



Now product p is:







  --->  x = N/2  



This is a local MAX value b/c  which is concave DOWN.