Question 538235
Take a number, x. If it adds to some other number to equal 150, then 150-x is that other number.<P>
We have x and 150-x, and their product must be as large as possible.<P>
{{{x(150-x)=-x^2 + 150x}}}<P>
Graph it, or remember that it will be a parabola opening down.<P>
Thus, when its derivative equals 0 {{{-2x+150=0}}} the function has its maximum.<P>
Subtract 150 from both sides.<P>
{{{-2x = -150}}}<P>
Divide both sides by -2<P>
{{{x-75}}}<P>
The product of the numbers {{{x*(150-x)}}} has its maximum value when x=75.  And when x=75 then 150-x = 150-75 = 75.<P>
The two numbers are 75.<P>
You could also solve this by looking at a much smaller number, like 6.<P>
What two real numbers whose sum is 6 have the maximum product?  <P>
Compare 3 and 3 with 1 and 5 with 4 and 2 with 6 and 0.  The largest product is 3*3.<P>
Look at 5.  The largest product comes from 2.5 * 2.5<P>
For 8 the largest product comes from 4*4.  <P>
By observation you can see that when the sum is a positive number, then the largest product comes from the number divided by 2.<P>
150/2=75.<P>
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