x^2-2x-3=0解：(x-3)(x+1)=0x1=3，x2=-1
x²-2x-3=0(x-3)(x+1)=0x1=3x2=-1
x^2-2x-3=0(x+1)*(x-3)=0x=-1或x=3
楼上正解 高明
