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D( b )
b = 0
b = 0
b = 0
b in (-oo:0) U (0:+oo)
(9/4)*b = 12/b+4 // - 12/b+4
(9/4)*b-(12/b)-4 = 0
(9/4)*b-12*b^-1-4 = 0
9/4*b^1-12*b^-1-4*b^0 = 0
(9/4*b^2-4*b^1-12*b^0)/(b^1) = 0 // * b^2
b^1*(9/4*b^2-4*b^1-12*b^0) = 0
b^1
(9/4)*b^2-4*b-12 = 0
(9/4)*b^2-4*b-12 = 0
DELTA = (-4)^2-(-12*4*(9/4))
DELTA = 124
DELTA > 0
b = (124^(1/2)+4)/(2*(9/4)) or b = (4-124^(1/2))/(2*(9/4))
b = 2/9*(2*31^(1/2)+4) or b = 2/9*(4-2*31^(1/2))
b in { 2/9*(4-2*31^(1/2)), 2/9*(2*31^(1/2)+4)}
b in { 2/9*(4-2*31^(1/2)), 2/9*(2*31^(1/2)+4) }
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