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D( k )
k = 0
k = 0
k = 0
k in (-oo:0) U (0:+oo)
(10*k^2-(78*k)-26)/k-8 = 0
(10*k^2-78*k-26)/k-8 = 0
(10*k^2-78*k-26)/k+(-8*k)/k = 0
10*k^2-78*k-8*k-26 = 0
10*k^2-86*k-26 = 0
10*k^2-86*k-26 = 0
2*(5*k^2-43*k-13) = 0
5*k^2-43*k-13 = 0
DELTA = (-43)^2-(-13*4*5)
DELTA = 2109
DELTA > 0
k = (2109^(1/2)+43)/(2*5) or k = (43-2109^(1/2))/(2*5)
k = (2109^(1/2)+43)/10 or k = (43-2109^(1/2))/10
2*(k-((43-2109^(1/2))/10))*(k-((2109^(1/2)+43)/10)) = 0
(2*(k-((43-2109^(1/2))/10))*(k-((2109^(1/2)+43)/10)))/k = 0
(2*(k-((43-2109^(1/2))/10))*(k-((2109^(1/2)+43)/10)))/k = 0 // * k
2*(k-((43-2109^(1/2))/10))*(k-((2109^(1/2)+43)/10)) = 0
( k-((2109^(1/2)+43)/10) )
k-((2109^(1/2)+43)/10) = 0 // + (2109^(1/2)+43)/10
k = (2109^(1/2)+43)/10
( k-((43-2109^(1/2))/10) )
k-((43-2109^(1/2))/10) = 0 // + (43-2109^(1/2))/10
k = (43-2109^(1/2))/10
k in { (2109^(1/2)+43)/10, (43-2109^(1/2))/10 }
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