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D( r )
r = 0
r-9 = 0
r = 0
r = 0
r-9 = 0
r-9 = 0
r-9 = 0 // + 9
r = 9
r in (-oo:0) U (0:9) U (9:+oo)
5/(r-9) = 8/r+5 // - 8/r+5
5/(r-9)-(8/r)-5 = 0
5/(r-9)-8*r^-1-5 = 0
5/(r-9)-8/r-5 = 0
(5*r)/(r*(r-9))+(-8*(r-9))/(r*(r-9))+(-5*r*(r-9))/(r*(r-9)) = 0
5*r-8*(r-9)-5*r*(r-9) = 0
45*r-5*r^2-3*r+72 = 0
42*r-5*r^2+72 = 0
42*r-5*r^2+72 = 0
42*r-5*r^2+72 = 0
DELTA = 42^2-(-5*4*72)
DELTA = 3204
DELTA > 0
r = (3204^(1/2)-42)/(-5*2) or r = (-3204^(1/2)-42)/(-5*2)
r = (6*89^(1/2)-42)/(-10) or r = (-6*89^(1/2)-42)/(-10)
(r-((6*89^(1/2)-42)/(-10)))*(r-((-6*89^(1/2)-42)/(-10))) = 0
((r-((6*89^(1/2)-42)/(-10)))*(r-((-6*89^(1/2)-42)/(-10))))/(r*(r-9)) = 0
((r-((6*89^(1/2)-42)/(-10)))*(r-((-6*89^(1/2)-42)/(-10))))/(r*(r-9)) = 0 // * r*(r-9)
(r-((6*89^(1/2)-42)/(-10)))*(r-((-6*89^(1/2)-42)/(-10))) = 0
( r-((-6*89^(1/2)-42)/(-10)) )
r-((-6*89^(1/2)-42)/(-10)) = 0 // + (-6*89^(1/2)-42)/(-10)
r = (-6*89^(1/2)-42)/(-10)
( r-((6*89^(1/2)-42)/(-10)) )
r-((6*89^(1/2)-42)/(-10)) = 0 // + (6*89^(1/2)-42)/(-10)
r = (6*89^(1/2)-42)/(-10)
r in { (-6*89^(1/2)-42)/(-10), (6*89^(1/2)-42)/(-10) }
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