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D( r )
r^4-(6*r^3) = 0
r^4-(6*r^3) = 0
r^4-(6*r^3) = 0
r^4-6*r^3 = 0
r^4-6*r^3 = 0
r^3*(r-6) = 0
r-6 = 0 // + 6
r = 6
r^3 = 0
1*r^3 = 0 // : 1
r^3 = 0
r = 0
r in (-oo:0) U (0:6) U (6:+oo)
(r^2-(8*r)-12)/(r^4-(6*r^3)) = 0
(r^2-8*r-12)/(r^4-6*r^3) = 0
r^2-8*r-12 = 0
r^2-8*r-12 = 0
DELTA = (-8)^2-(-12*1*4)
DELTA = 112
DELTA > 0
r = (112^(1/2)+8)/(1*2) or r = (8-112^(1/2))/(1*2)
r = (4*7^(1/2)+8)/2 or r = (8-4*7^(1/2))/2
(r-((8-4*7^(1/2))/2))*(r-((4*7^(1/2)+8)/2)) = 0
r^4-6*r^3 = 0
r^3*(r-6) = 0
r-6 = 0 // + 6
r = 6
r^3*(r-6) = 0
((r-((8-4*7^(1/2))/2))*(r-((4*7^(1/2)+8)/2)))/(r^3*(r-6)) = 0
( r-((4*7^(1/2)+8)/2) )
r-((4*7^(1/2)+8)/2) = 0 // + (4*7^(1/2)+8)/2
r = (4*7^(1/2)+8)/2
( r-((8-4*7^(1/2))/2) )
r-((8-4*7^(1/2))/2) = 0 // + (8-4*7^(1/2))/2
r = (8-4*7^(1/2))/2
r in { (4*7^(1/2)+8)/2, (8-4*7^(1/2))/2 }
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