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D( z )
z-7 = 0
z-5 = 0
z-7 = 0
z-7 = 0
z-7 = 0 // + 7
z = 7
z-5 = 0
z-5 = 0
z-5 = 0 // + 5
z = 5
z in (-oo:5) U (5:7) U (7:+oo)
6/(z-7)-(4/(z-5))-((2*z)/(z-7)) = 0
6/(z-7)-4*(z-5)^-1-2*z*(z-7)^-1 = 0
6/(z-7)-4/(z-5)+(-2*z)/(z-7) = 0
(6*(z-5))/((z-7)*(z-5))+(-4*(z-7))/((z-7)*(z-5))+(-2*z*(z-5))/((z-7)*(z-5)) = 0
6*(z-5)-4*(z-7)-2*z*(z-5) = 0
2*z-2*z^2+10*z-2 = 0
12*z-2*z^2-2 = 0
12*z-2*z^2-2 = 0
2*(6*z-z^2-1) = 0
6*z-z^2-1 = 0
DELTA = 6^2-(-1*(-1)*4)
DELTA = 32
DELTA > 0
z = (32^(1/2)-6)/(-1*2) or z = (-32^(1/2)-6)/(-1*2)
z = (4*2^(1/2)-6)/(-2) or z = (-4*2^(1/2)-6)/(-2)
2*(z-((4*2^(1/2)-6)/(-2)))*(z-((-4*2^(1/2)-6)/(-2))) = 0
(2*(z-((4*2^(1/2)-6)/(-2)))*(z-((-4*2^(1/2)-6)/(-2))))/((z-7)*(z-5)) = 0
(2*(z-((4*2^(1/2)-6)/(-2)))*(z-((-4*2^(1/2)-6)/(-2))))/((z-7)*(z-5)) = 0 // * (z-7)*(z-5)
2*(z-((4*2^(1/2)-6)/(-2)))*(z-((-4*2^(1/2)-6)/(-2))) = 0
( 2 )
2 = 0
z belongs to the empty set
( z-((-4*2^(1/2)-6)/(-2)) )
z-((-4*2^(1/2)-6)/(-2)) = 0 // + (-4*2^(1/2)-6)/(-2)
z = (-4*2^(1/2)-6)/(-2)
( z-((4*2^(1/2)-6)/(-2)) )
z-((4*2^(1/2)-6)/(-2)) = 0 // + (4*2^(1/2)-6)/(-2)
z = (4*2^(1/2)-6)/(-2)
z in { (-4*2^(1/2)-6)/(-2), (4*2^(1/2)-6)/(-2) }
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