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D( x )
x = 0
x = 0
x = 0
x in (-oo:0) U (0:+oo)
12-(7*x) = 1/x // - 1/x
12-(7*x)-(1/x) = 0
12-7*x-x^-1 = 0
12*x^0-7*x^1-1*x^-1 = 0
(12*x^1-7*x^2-1*x^0)/(x^1) = 0 // * x^2
x^1*(12*x^1-7*x^2-1*x^0) = 0
x^1
12*x-7*x^2-1 = 0
12*x-7*x^2-1 = 0
DELTA = 12^2-(-7*(-1)*4)
DELTA = 116
DELTA > 0
x = (116^(1/2)-12)/(-7*2) or x = (-116^(1/2)-12)/(-7*2)
x = (2*29^(1/2)-12)/(-14) or x = (-2*29^(1/2)-12)/(-14)
x in { (2*29^(1/2)-12)/(-14), (-2*29^(1/2)-12)/(-14)}
x in { (2*29^(1/2)-12)/(-14), (-2*29^(1/2)-12)/(-14) }
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