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k in (-oo:+oo)
2*(2-4*k) = -12 // + 12
2*(2-4*k)+12 = 0
2*(2-4*k)+12 = 0
16-8*k = 0
16-8*k = 0
16-8*k = 0 // - 16
-8*k = -16 // : -8
k = -16/(-8)
k = 2
k = 2
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