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N in (-oo:+oo)
42/12 = N/2 // - N/2
42/12-(N/2) = 0
7/2-1/2*N = 0 // - 7/2
-1/2*N = -7/2 // : -1/2
N = -7/2/(-1/2)
N = 7
N = 7
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