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D( r )
r = 0
r = 0
r = 0
r in (-oo:0) U (0:+oo)
(4*r-2)/r = 7/6 // - 7/6
(4*r-2)/r-(7/6) = 0
(4*r-2)/r-7/6 = 0
(6*(4*r-2))/(6*r)+(-7*r)/(6*r) = 0
6*(4*r-2)-7*r = 0
17*r-12 = 0
(17*r-12)/(6*r) = 0
(17*r-12)/(6*r) = 0 // * 6*r
17*r-12 = 0
17*r-12 = 0 // + 12
17*r = 12 // : 17
r = 12/17
r = 12/17
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