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D( r )
r-2 = 0
r-2 = 0
r-2 = 0
r-2 = 0 // + 2
r = 2
r in (-oo:2) U (2:+oo)
2*r-(4/(r-2)) = 0
2*r-4*(r-2)^-1 = 0
2*r-4/(r-2) = 0
(2*r*(r-2))/(r-2)-4/(r-2) = 0
2*r*(r-2)-4 = 0
2*r^2-4*r-4 = 0
2*r^2-4*r-4 = 0
2*(r^2-2*r-2) = 0
r^2-2*r-2 = 0
DELTA = (-2)^2-(-2*1*4)
DELTA = 12
DELTA > 0
r = (12^(1/2)+2)/(1*2) or r = (2-12^(1/2))/(1*2)
r = (2*3^(1/2)+2)/2 or r = (2-2*3^(1/2))/2
2*(r-((2-2*3^(1/2))/2))*(r-((2*3^(1/2)+2)/2)) = 0
(2*(r-((2-2*3^(1/2))/2))*(r-((2*3^(1/2)+2)/2)))/(r-2) = 0
(2*(r-((2-2*3^(1/2))/2))*(r-((2*3^(1/2)+2)/2)))/(r-2) = 0 // * r-2
2*(r-((2-2*3^(1/2))/2))*(r-((2*3^(1/2)+2)/2)) = 0
( r-((2*3^(1/2)+2)/2) )
r-((2*3^(1/2)+2)/2) = 0 // + (2*3^(1/2)+2)/2
r = (2*3^(1/2)+2)/2
( r-((2-2*3^(1/2))/2) )
r-((2-2*3^(1/2))/2) = 0 // + (2-2*3^(1/2))/2
r = (2-2*3^(1/2))/2
r in { (2*3^(1/2)+2)/2, (2-2*3^(1/2))/2 }
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