Two industrial plants, š“š“ and šµšµ, are located 15 miles per apart and emit 75 ppm (parts per
million) and 300 ppm of particular matter, respectively. Each part is surrounded by a restricted
area of radius 1 mile in which no housing is allowed, and the concentration of pollutant arriving
at any other point šš from each plant decreases with the reciprocal of the distance between that
plant and šš. Where should a house be located on a road joining the two plants to minimize the
total pollution arriving from both plants?
LetĀ "x"Ā denote the distance between the house and Plant A in miles. Then the distance between the house and Plant B will beĀ "15-x" miles.
Also, since Plant A has a restricted area of 1 mile around it and Plant B has a restricted area of 1 mile around it, therefore "1\\leq x \\leq14."
The smog from plantĀ AĀ is "\\dfrac{75}{x}." The smog from plantĀ BĀ is "\\dfrac{300}{15-x}."
Total pollution arriving from both plants is
Find the first derivative with respeect to "x"
"=-\\dfrac{75}{x^2}+\\dfrac{300}{(15-x)^2}"
Find the critical number(s)
"4x^2=(15-x)^2"
"3x^2+30x-225=0"
"x^2+10x-75=0"
"(x+5)^2=100"
"x_1=-15, x_2=5"
Critical numbers: "-15, 5."
Since "1\\leq x\\leq 14," we take "5" as the critical number.
"f(14)=\\dfrac{75}{14}+\\dfrac{300}{15-14}=305\\dfrac{5}{14}"
"f(5)=\\dfrac{75}{5}+\\dfrac{300}{15-5}=45"
"f(1)<f(5)<f(14)."
Therefore, the house should be locatedĀ 5 miles from plantĀ A.
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