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D( u )
u = 0
u = 0
u = 0
u in (-oo:0) U (0:+oo)
4-8/u = (-7/4)*u+2+16 // - (-7/4)*u+2+16
4-((-7/4)*u)-8/u-16-2 = 0
(7/4)*u-8/u-16-2+4 = 0
7/4*u^1-8*u^-1-14*u^0 = 0
(7/4*u^2-14*u^1-8*u^0)/(u^1) = 0 // * u^2
u^1*(7/4*u^2-14*u^1-8*u^0) = 0
u^1
(7/4)*u^2-14*u-8 = 0
(7/4)*u^2-14*u-8 = 0
DELTA = (-14)^2-(-8*4*(7/4))
DELTA = 252
DELTA > 0
u = (252^(1/2)+14)/(2*(7/4)) or u = (14-252^(1/2))/(2*(7/4))
u = 2/7*(6*7^(1/2)+14) or u = 2/7*(14-6*7^(1/2))
u in { 2/7*(14-6*7^(1/2)), 2/7*(6*7^(1/2)+14)}
u in { 2/7*(14-6*7^(1/2)), 2/7*(6*7^(1/2)+14) }
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