x²-4x-5=0
Δ=(-4)²-4·1·(-5)
Δ=16+20
Δ=36
√Δ=√36=6
x₁=(4-6)/(2·1)=-2/2=-1
x₂=(4+6)/(2·1)=10/2=5
(x-3)(x+2)=2x(x-2)-2x
x²+2x-3x-6=2x²-4x-2x
x²-x-6=x²-6x
x²-x-6-2x²+6x=0
x²-2x²-x+6x-6=0
-x²+5x-6=0
Δ=5²-4·(-1)·(-6)
Δ=25-24
Δ=1
√Δ=√1=1
x₁=(-5-1)/(2·(-1))=-6/-2=3
x₂=(-5+1)/(2·(-1))=-4/-2=2
