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D( x )
2*x+1 = 0
x = 0
2*x+1 = 0
2*x+1 = 0
2*x+1 = 0 // - 1
2*x = -1 // : 2
x = -1/2
x = 0
x = 0
x in (-oo:-1/2) U (-1/2:0) U (0:+oo)
(2*x+1)/x+x/(2*x+1) = 58/21 // - 58/21
(2*x+1)/x+x/(2*x+1)-(58/21) = 0
(2*x+1)/x+x/(2*x+1)-58/21 = 0
(21*(2*x+1)^2)/(21*x*(2*x+1))+(21*x^2)/(21*x*(2*x+1))+(-58*x*(2*x+1))/(21*x*(2*x+1)) = 0
21*(2*x+1)^2-58*x*(2*x+1)+21*x^2 = 0
105*x^2-116*x^2+84*x-58*x+21 = 0
26*x-11*x^2+21 = 0
26*x-11*x^2+21 = 0
26*x-11*x^2+21 = 0
DELTA = 26^2-(-11*4*21)
DELTA = 1600
DELTA > 0
x = (1600^(1/2)-26)/(-11*2) or x = (-1600^(1/2)-26)/(-11*2)
x = -7/11 or x = 3
(x+7/11)*(x-3) = 0
((x+7/11)*(x-3))/(21*x*(2*x+1)) = 0
((x+7/11)*(x-3))/(21*x*(2*x+1)) = 0 // * 21*x*(2*x+1)
(x+7/11)*(x-3) = 0
( x+7/11 )
x+7/11 = 0 // - 7/11
x = -7/11
( x-3 )
x-3 = 0 // + 3
x = 3
x in { -7/11, 3 }
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