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D( k )
k^2 = 0
k = 0
k^2 = 0
k^2 = 0
1*k^2 = 0 // : 1
k^2 = 0
k = 0
k = 0
k = 0
k in (-oo:0) U (0:+oo)
5-(4/k)-(1/(k^2)) = 0
5-4*k^-1-k^-2 = 0
t_1 = k^-1
5-1*t_1^2-4*t_1^1 = 0
5-t_1^2-4*t_1 = 0
DELTA = (-4)^2-(-1*4*5)
DELTA = 36
DELTA > 0
t_1 = (36^(1/2)+4)/(-1*2) or t_1 = (4-36^(1/2))/(-1*2)
t_1 = -5 or t_1 = 1
t_1 = -5
k^-1+5 = 0
1*k^-1 = -5 // : 1
k^-1 = -5
-1 < 0
1/(k^1) = -5 // * k^1
1 = -5*k^1 // : -5
-1/5 = k^1
k = -1/5
t_1 = 1
k^-1-1 = 0
1*k^-1 = 1 // : 1
k^-1 = 1
-1 < 0
1/(k^1) = 1 // * k^1
1 = 1*k^1 // : 1
1 = k^1
k = 1
k in { -1/5, 1 }
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