x²+3x+5=7,x²=2-3x,x²+3x-2=0,(x+3/2)²=2+9/4=17/4,x=-3/2±√17/2
3x²-9x-2=6-9x-9x-2=4-18x=4-18(-3/2±√17/2)=31±9√17