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D( r )
r^2-(5*r)-6 = 0
r+1 = 0
r^2-(5*r)-6 = 0
r^2-(5*r)-6 = 0
r^2-5*r-6 = 0
r^2-5*r-6 = 0
DELTA = (-5)^2-(-6*1*4)
DELTA = 49
DELTA > 0
r = (49^(1/2)+5)/(1*2) or r = (5-49^(1/2))/(1*2)
r = 6 or r = -1
r+1 = 0
r+1 = 0
r+1 = 0 // - 1
r = -1
r in (-oo:-1) U (-1:6) U (6:+oo)
1/(r+1) = 4/(r+1)-(6/(r^2-(5*r)-6)) // - 4/(r+1)-(6/(r^2-(5*r)-6))
1/(r+1)-(4/(r+1))+6/(r^2-(5*r)-6) = 0
1/(r+1)-4*(r+1)^-1+6/(r^2-5*r-6) = 0
1/(r+1)-4/(r+1)+6/(r^2-5*r-6) = 0
r^2-5*r-6 = 0
r^2-5*r-6 = 0
r^2-5*r-6 = 0
DELTA = (-5)^2-(-6*1*4)
DELTA = 49
DELTA > 0
r = (49^(1/2)+5)/(1*2) or r = (5-49^(1/2))/(1*2)
r = 6 or r = -1
(r+1)*(r-6) = 0
1/(r+1)-4/(r+1)+6/((r+1)*(r-6)) = 0
1/(r+1)-4/(r+1)+6/(r+1) = 0
1-4+6 = 0
6-3 = 0
3 = 0
3/(r+1) = 0
3/(r+1) = 0 // * r+1
3 = 0
r belongs to the empty set
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