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Find two positive numbers for which the product is 196 and the sum of the first plus four times the second is a minimum. ONE of these numbers is B) 14 C) 12 D) 8 E) 7

Answer :

Minimum  number is 33+4*6= 57

Give us two positive numbers, x and y.

196 is the result: x*y = 19

The minimum is the product of the first plus four times the second: x + 4y.

The first equation results in y = 196/x. Put that into the second equation as a replacement:

x + 4y = x + 4(196/x) = x + 784/x

Taking the first derivative now, we can solve for x by setting it to zero.

d(x + 784/x)/dx = 1 - 784/[tex]x^{2}[/tex]

0 = 1 - 784/[tex]x^{2}[/tex]

0 = [tex]x^{2}[/tex]- 784 [[tex]x^{2}[/tex] multiplied on both sides]

784 = [tex]x^{2}[/tex]

[tex]\sqrt{784}[/tex] = [tex]\sqrt{x^{2} }[/tex]

Y = 196/x = 7 since we want a positive integer, hence x = 28

The factors of 196 are 196*1, 99*2, 66*3, 6*33,22*19, and 11*18 as a check.

196 + 4*1 = 200

99 + 4*2 = 107

66 + 4*3 = 78

33+4*6= 57

22 + 4*19 = 98

11 + 4*18=82

In fact, 33+4*6= 57 is minimum.

To learn more about factors:

https://brainly.com/question/14209188

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