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D( r )
r = 0
r = 0
r = 0
r in (-oo:0) U (0:+oo)
1/r-5 = (7/2)*r // - (7/2)*r
1/r-((7/2)*r)-5 = 0
(-7/2)*r+1/r-5 = 0
1*r^-1-7/2*r^1-5*r^0 = 0
(1*r^0-7/2*r^2-5*r^1)/(r^1) = 0 // * r^2
r^1*(1*r^0-7/2*r^2-5*r^1) = 0
r^1
(-7/2)*r^2-5*r+1 = 0
(-7/2)*r^2-5*r+1 = 0
DELTA = (-5)^2-(1*4*(-7/2))
DELTA = 39
DELTA > 0
r = (39^(1/2)+5)/(2*(-7/2)) or r = (5-39^(1/2))/(2*(-7/2))
r = (39^(1/2)+5)/(-7) or r = (5-39^(1/2))/(-7)
r in { (39^(1/2)+5)/(-7), (5-39^(1/2))/(-7)}
r in { (39^(1/2)+5)/(-7), (5-39^(1/2))/(-7) }
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