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D( w )
w = 0
w = 0
w = 0
w in (-oo:0) U (0:+oo)
w/w-(((2*w)/2)*w)-5-4 = w-((2/2)*w^2)-(13*w)+20 // - w-((2/2)*w^2)-(13*w)+20
(2/2)*w^2-(((2*w)/2)*w)-w+13*w+w/w-20-5-4 = 0
(2/2)*w^2-w^2-w+13*w+w/w-20-5-4 = 0
12*w-28 = 0 // + 28
12*w = 28 // : 12
w = 28/12
w = 7/3
w = 7/3
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