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k in (-oo:+oo)
-(4*k)-1 = -13 // + 13
13-(4*k)-1 = 0
13-4*k-1 = 0
12-4*k = 0 // - 12
-4*k = -12 // : -4
k = -12/(-4)
k = 3
k = 3
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