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43 votes
Find two positive numbers whose product is 192 and their sum is a minimum.

User Lupchiazoem
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1 Answer

12 votes
12 votes

Answer:

8√3

Explanation:

Let a, b = the positive numbers, and the sum = s,

(1)---- ab = 192

(2)--- a + b = s

Since we want to find the minimum sum, we'll have to substitute one of the variables (either a or b) from (1) to (2), I'll choose b,

From (1), b = 192/a

Substitute b = 192/a into (2),

s = a + 192/a

Now, we are able to use a concept of calculus (maximum & minimum) to solve it, just remember 2 steps in finding the values of x in maxima minima question:

1) find dy/dx

2) Find x from dy/dx = 0

ds/da = 1 - 192/

When ds/da = 0,

1 - 192/ = 0

= 192

a = ±192

a = 83 , -83

Since a is positive, a = 83

Substitute a into (1),

b = 192/(83)

b = 83

Therefore, the two positive numbers are 8√3... and 8√3

User FAQi
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