document.write( "Question 538235: Of all the real numbers whose sum is 150, find the two which have the maximum product. \n" ); document.write( "
Algebra.Com's Answer #353146 by fcabanski(1391)\"\" \"About 
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Take a number, x. If it adds to some other number to equal 150, then 150-x is that other number.


\n" ); document.write( "We have x and 150-x, and their product must be as large as possible.


\n" ); document.write( "\"x%28150-x%29=-x%5E2+%2B+150x\"


\n" ); document.write( "Graph it, or remember that it will be a parabola opening down.


\n" ); document.write( "Thus, when its derivative equals 0 \"-2x%2B150=0\" the function has its maximum.


\n" ); document.write( "Subtract 150 from both sides.


\n" ); document.write( "\"-2x+=+-150\"


\n" ); document.write( "Divide both sides by -2


\n" ); document.write( "\"x-75\"


\n" ); document.write( "The product of the numbers \"x%2A%28150-x%29\" has its maximum value when x=75. And when x=75 then 150-x = 150-75 = 75.


\n" ); document.write( "The two numbers are 75.


\n" ); document.write( "You could also solve this by looking at a much smaller number, like 6.


\n" ); document.write( "What two real numbers whose sum is 6 have the maximum product?


\n" ); document.write( "Compare 3 and 3 with 1 and 5 with 4 and 2 with 6 and 0. The largest product is 3*3.


\n" ); document.write( "Look at 5. The largest product comes from 2.5 * 2.5


\n" ); document.write( "For 8 the largest product comes from 4*4.


\n" ); document.write( "By observation you can see that when the sum is a positive number, then the largest product comes from the number divided by 2.


\n" ); document.write( "150/2=75.


\n" ); document.write( "

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