x1+x2=4/5x1x2=-1/5所以1/x1+1/x2=(x1+x2)/(x1x2)=-4(x1+x2)²=(4/5)²x1²+2x1x2+x2²=16/25x1²+x2²=16/25-2x1x2=26/25所以x2/x1+x1/x2=(x2²+x1²)/(x1x2)=-26/5为什么？ 所以1/x1+1/x2=(x1+x2)/(x1x2)=-4通分都不懂？？？