{x²+7x+12≥0 x1+x2=-7 U x1*x2=12 x1=-4 U x2=-3 ⇒x≤-4 U x≥-3
{x²-2x-3>0 x1+x2=2 U x1*x2=-3 x1=-1 U x2=3⇒x<-1 U x>3
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---------[-4]--------------[-3]-------------(-1)-----------(3)--------------
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x∈(-∞;-4] U [-3;-1) U (3;∞)