令x²+3x=aa-20/a=8a²-8a-20=0(a-10)(a+2)=0a=10,a=-2x²+3x=10x²+3x-10=0(x+5)(x-2)=0x=-5,x=2x²+3x=-2x²+3x+2=0(x+1)(x+2)=0x=-1,x=-2x=-5,x=2,x=-1,x=-2