Question

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

Answer 1

Answer:

8√3

Step-by-step 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/a²

When ds/da = 0,

1 - 192/a² = 0

a² = 192

a = ±√192

a = 8√3 , -8√3

Since a is positive, a = 8√3

Substitute a into (1),

b = 192/(8√3)

b = 8√3

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