



 
Hi David, You want to maximize the product of x and y which is
You are also told the the sum of x and y is S so x + y = S. Solving this equation for y gives
Substitute this value for y into the product expression to get
At this point use the distributive law which says for any numbers a, b and c, a × (b + c) = a × b + a × c. Thus
I hope this helps,  


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