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What is the minimum sum of the numbers if the product of 2 numbers is 81?
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The product of two numbers is 81. If one of the numbers is 81, the other number is 81/x.
The sum of the numbers is S = x + 81/x. To find the minimum value of S, S' = 0 has to be solved for x.
S' = 1 - 81/x^2
1 - 81/x^2 = 0
=> x^2 = 81
=> x = 9 and x = -9
An assumption has to be made that the numbers are positive to be able to determine the minimum sum.
The minimum sum of the numbers is 18.
Posted by justaguide on August 29, 2012 at 5:09 PM (Answer #1)
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