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