1.3x²-1=8x
x=(4±√13)/3
2.x²-3x-1=0
x=(3±√13)/2
3.(2x+1)(x-3)=-6x
2x²+x-3=0
x=-1.5或x=1
4.x=0.4-0.6x²
3x²+5x-2=0
x=1/3或x=-2