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D( r )
r = 0
r = 0
r = 0
r in (-oo:0) U (0:+oo)
8/9 = r-(17/r) // - r-(17/r)
17/r-r+8/9 = 0
17*r^-1-1*r^1+8/9*r^0 = 0
(8/9*r^1-1*r^2+17*r^0)/(r^1) = 0 // * r^2
r^1*(8/9*r^1-1*r^2+17*r^0) = 0
r^1
(8/9)*r-r^2+17 = 0
(8/9)*r-r^2+17 = 0
DELTA = (8/9)^2-(-1*4*17)
DELTA = 5572/81
DELTA > 0
r = ((5572/81)^(1/2)-(8/9))/(-1*2) or r = (-(8/9)-(5572/81)^(1/2))/(-1*2)
r = ((5572/81)^(1/2)-8/9)/(-2) or r = ((5572/81)^(1/2)+8/9)/2
r in { ((5572/81)^(1/2)-8/9)/(-2), ((5572/81)^(1/2)+8/9)/2}
r in { ((5572/81)^(1/2)-8/9)/(-2), ((5572/81)^(1/2)+8/9)/2 }
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