3x²-9x=-2x²-3x=-2/3x²-3x+9/4=-2/3+9/4(x-3/2)²=19/12x-3/2=±√57/6x=(9-√57)/6，x=(9+√57)/6
3x^2-9x=-2x^2-3x=-2/3x^2-3x=（3/2)^2=-2/3 +(3/2)^2(x-3/2)^2=19/12x-3/2=±√57/6x=±√57/6+3/2
