1. ax²+bx+c=0, Δ=b²-4ac, Δ<0 ecuatia nu are solutii reale, Δ≥0, ecuatia are solutii reale
x²+3x+4=0
a=1, b=3, c=4, Δ=9-4*1*4=9-16=-7<0, ecuatia nu are solutii reale A
2. x²+6x-7=0, x1,2=(-b+-√Δ)/2a
a=1, b=6, c=-7
Δ=36+28=64, √Δ=8
x1=(-6+8)/2=1
x2=(-6-8)/2=-7
S={-7, 1} B