Question 3420
Let the 2 numbers be x and y.


so, we are told that x+y=40 --eqn1
and that xy is to be a maximum.


so we have the function f(x) = xy. Now get rid of y by using eqn1 (written as y = 40-x... so f(x) = x(40-x)...easy enough?


We are told to find those 2 numbers that have the largest product (ie 1x39, 2x38, 3x37 etc)...


dy/dx = 40 - 2x = 0
so, x=20
so therefore, y must be 20 too


this is the answer: x=y=20


jon