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D( k )
k = 0
k = 0
k = 0
k in (-oo:0) U (0:+oo)
-3 = -12/k // + -12/k
-(-12/k)-3 = 0
12*k^-1-3 = 0
12*k^-1 = 3 // : 12
k^-1 = 1/4
-1 < 0
1/(k^1) = 1/4 // * k^1
1 = 1/4*k^1 // : 1/4
4 = k^1
k = 4
k = 4
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