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D( x )
x = 0
x = 0
x = 0
x in (-oo:0) U (0:+oo)
8*x = 30/x // - 30/x
8*x-(30/x) = 0
8*x-30*x^-1 = 0
8*x^1-30*x^-1 = 0
(8*x^2-30*x^0)/(x^1) = 0 // * x^2
x^1*(8*x^2-30*x^0) = 0
x^1
8*x^2-30 = 0
8*x^2-30 = 0
DELTA = 0^2-(-30*4*8)
DELTA = 960
DELTA > 0
x = (960^(1/2)+0)/(2*8) or x = (0-960^(1/2))/(2*8)
x = (1*15^(1/2))/2 or x = (-15^(1/2))/2
x in { (-15^(1/2))/2, (1*15^(1/2))/2}
x in { (-15^(1/2))/2, (1*15^(1/2))/2 }
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