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D( x )
9*x+21 = 0
x = 0
x+9 = 0
9*x+21 = 0
9*x+21 = 0
9*x+21 = 0 // - 21
9*x = -21 // : 9
x = -21/9
x = -7/3
x = 0
x = 0
x+9 = 0
x+9 = 0
x+9 = 0 // - 9
x = -9
x in (-oo:-9) U (-9:-7/3) U (-7/3:0) U (0:+oo)
(1/x)*(1/(x+9)) = 17/(9*x+21) // - 17/(9*x+21)
(1/x)*(1/(x+9))-(17/(9*x+21)) = 0
(1/x)*(1/(x+9))-17*(9*x+21)^-1 = 0
(1*x^-1)/(x+9)-17/(9*x+21) = 0
(1*x^-1*(9*x+21))/((x+9)*(9*x+21))+(-17*(x+9))/((x+9)*(9*x+21)) = 0
1*x^-1*(9*x+21)-17*(x+9) = 0
21*x^-1-17*x-144 = 0
21*x^-1-17*x-144 = 0
21*x^-1-17*x^1-144*x^0 = 0
(21*x^0-17*x^2-144*x^1)/(x^1) = 0 // * x^2
x^1*(21*x^0-17*x^2-144*x^1) = 0
x^1
21-17*x^2-144*x = 0
21-17*x^2-144*x = 0
DELTA = (-144)^2-(-17*4*21)
DELTA = 22164
DELTA > 0
x = (22164^(1/2)+144)/(-17*2) or x = (144-22164^(1/2))/(-17*2)
x = (2*5541^(1/2)+144)/(-34) or x = (144-2*5541^(1/2))/(-34)
x in { (2*5541^(1/2)+144)/(-34), (144-2*5541^(1/2))/(-34)}
(x-((2*5541^(1/2)+144)/(-34)))*(x-((144-2*5541^(1/2))/(-34))) = 0
((x-((2*5541^(1/2)+144)/(-34)))*(x-((144-2*5541^(1/2))/(-34))))/((x+9)*(9*x+21)) = 0
((x-((2*5541^(1/2)+144)/(-34)))*(x-((144-2*5541^(1/2))/(-34))))/((x+9)*(9*x+21)) = 0 // * (x+9)*(9*x+21)
(x-((2*5541^(1/2)+144)/(-34)))*(x-((144-2*5541^(1/2))/(-34))) = 0
( x-((144-2*5541^(1/2))/(-34)) )
x-((144-2*5541^(1/2))/(-34)) = 0 // + (144-2*5541^(1/2))/(-34)
x = (144-2*5541^(1/2))/(-34)
( x-((2*5541^(1/2)+144)/(-34)) )
x-((2*5541^(1/2)+144)/(-34)) = 0 // + (2*5541^(1/2)+144)/(-34)
x = (2*5541^(1/2)+144)/(-34)
x in { (144-2*5541^(1/2))/(-34), (2*5541^(1/2)+144)/(-34) }
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