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D( u )
u+4 = 0
u-1 = 0
u+4 = 0
u+4 = 0
u+4 = 0 // - 4
u = -4
u-1 = 0
u-1 = 0
u-1 = 0 // + 1
u = 1
u in (-oo:-4) U (-4:1) U (1:+oo)
3/(u-1)+4 = 7/(u+4) // - 7/(u+4)
3/(u-1)-(7/(u+4))+4 = 0
3/(u-1)-7*(u+4)^-1+4 = 0
3/(u-1)-7/(u+4)+4 = 0
(3*(u+4))/((u-1)*(u+4))+(-7*(u-1))/((u-1)*(u+4))+(4*(u-1)*(u+4))/((u-1)*(u+4)) = 0
3*(u+4)-7*(u-1)+4*(u-1)*(u+4) = 0
4*u^2-4*u+12*u-16+19 = 0
4*u^2+8*u+3 = 0
4*u^2+8*u+3 = 0
4*u^2+8*u+3 = 0
DELTA = 8^2-(3*4*4)
DELTA = 16
DELTA > 0
u = (16^(1/2)-8)/(2*4) or u = (-16^(1/2)-8)/(2*4)
u = -1/2 or u = -3/2
(u+3/2)*(u+1/2) = 0
((u+3/2)*(u+1/2))/((u-1)*(u+4)) = 0
((u+3/2)*(u+1/2))/((u-1)*(u+4)) = 0 // * (u-1)*(u+4)
(u+3/2)*(u+1/2) = 0
( u+1/2 )
u+1/2 = 0 // - 1/2
u = -1/2
( u+3/2 )
u+3/2 = 0 // - 3/2
u = -3/2
u in { -1/2, -3/2 }
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