2x²-6x-6=0
两边除以2,得
x²-3x-3=0
∵a=1,b=-3,c=-3
Δ=(-3)²－4×1×(-3)
=9＋12
=21
∴x=½(3±√21)
x1=½(3+√21),x2=½(3-√21)