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D( w )
w = 0
w = 0
w = 0
w in (-oo:0) U (0:+oo)
(-1/5)*w+3+20 = 7/w+4 // - 7/w+4
(-1/5)*w-(7/w)-4+3+20 = 0
(-1/5)*w-7*w^-1-4+3+20 = 0
19*w^0-1/5*w^1-7*w^-1 = 0
(19*w^1-1/5*w^2-7*w^0)/(w^1) = 0 // * w^2
w^1*(19*w^1-1/5*w^2-7*w^0) = 0
w^1
(-1/5)*w^2+19*w-7 = 0
(-1/5)*w^2+19*w-7 = 0
DELTA = 19^2-(-7*4*(-1/5))
DELTA = 1777/5
DELTA > 0
w = ((1777/5)^(1/2)-19)/(2*(-1/5)) or w = (-(1777/5)^(1/2)-19)/(2*(-1/5))
w = -5/2*((1777/5)^(1/2)-19) or w = 5/2*((1777/5)^(1/2)+19)
w in { -5/2*((1777/5)^(1/2)-19), 5/2*((1777/5)^(1/2)+19)}
w in { -5/2*((1777/5)^(1/2)-19), 5/2*((1777/5)^(1/2)+19) }
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