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D( r )
r = 0
r = 0
r = 0
r in (-oo:0) U (0:+oo)
12/r = (4/0.5)*r-1 // - (4/0.5)*r-1
12/r-((4/0.5)*r)+1 = 0
12/r-8*r+1 = 0
12*r^-1-8*r^1+1*r^0 = 0
(1*r^1-8*r^2+12*r^0)/(r^1) = 0 // * r^2
r^1*(1*r^1-8*r^2+12*r^0) = 0
r^1
r-8*r^2+12 = 0
r-8*r^2+12 = 0
DELTA = 1^2-(-8*4*12)
DELTA = 385
DELTA > 0
r = (385^(1/2)-1)/(-8*2) or r = (-385^(1/2)-1)/(-8*2)
r = (385^(1/2)-1)/(-16) or r = (385^(1/2)+1)/16
r in { (385^(1/2)-1)/(-16), (385^(1/2)+1)/16}
r in { (385^(1/2)-1)/(-16), (385^(1/2)+1)/16 }
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