1。|x1-x2|=√(x1-x2)²=√[(x1+x2)²-4x1x2]=√[(-1)²-4×(-3)]=√13 2。x²+x-3=0x1²+x1-3=0x1²+x1=3 x1²+2x1+x2=x1²+x1+(x1+x2)=3-1=2