4x²+4x-16=0 Δ = 4²-4*4*(-16)=16+256=272=16*17 => √Δ=4√17;
x₁=(-4+4√17)/8=(√17-1)/2
x₂=(-4 -4√17)/8= - 4*(√17+1)/8=(√17+1)/2
x²-8x+7=0 Δ=64-4*1*7=64 - 28=36 => √Δ=6 ;
x₁=(8+6)/2 = 7
x₂=(8 - 6)/2= 1
x²+4x-12=0 Δ=16 - 4*1*(-12)=16+48=64 => √Δ=8 ;
x₁=(-4+8)/2 = 2
x₂=(-4-8)/2 = -6