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D( z )
2*z = 0
2*z = 0
2*z = 0
2*z = 0 // : 2
z = 0
z in (-oo:0) U (0:+oo)
(2*z^2-(12*z)-8)/(2*z) = 0
(2*z^2-12*z-8)/(2*z) = 0
2*z^2-12*z-8 = 0
2*(z^2-6*z-4) = 0
z^2-6*z-4 = 0
DELTA = (-6)^2-(-4*1*4)
DELTA = 52
DELTA > 0
z = (52^(1/2)+6)/(1*2) or z = (6-52^(1/2))/(1*2)
z = (2*13^(1/2)+6)/2 or z = (6-2*13^(1/2))/2
2*(z-((6-2*13^(1/2))/2))*(z-((2*13^(1/2)+6)/2)) = 0
(2*(z-((6-2*13^(1/2))/2))*(z-((2*13^(1/2)+6)/2)))/(2*z) = 0
( 2 )
2 = 0
z belongs to the empty set
( z-((2*13^(1/2)+6)/2) )
z-((2*13^(1/2)+6)/2) = 0 // + (2*13^(1/2)+6)/2
z = (2*13^(1/2)+6)/2
( z-((6-2*13^(1/2))/2) )
z-((6-2*13^(1/2))/2) = 0 // + (6-2*13^(1/2))/2
z = (6-2*13^(1/2))/2
z in { (2*13^(1/2)+6)/2, (6-2*13^(1/2))/2 }
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