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Δ=16-4*(-1)*21=100
x∈(-∞,-7) ∨ (-3,+∞)
Δ=100-4*(-5)*0=100
x∈(0,2)
W załączniku wykresy.
-x²-4x<-21
x(-x-4)<-21/:(-x-4)
x>
b) -5x²+10x>0
5x(-x+2)>0/:(-x+2)
5x<0/:5
x<0