(X1+1/X1)(X2+1/X2) =x1*x2+x1/x2+x2/x1+1/x1*x2 =x1*x2+(x1^2+x2^2)/(x1*x2)+1/x1*x2 =x1*x2+[(x1+x2)^2-2x1*x2]/(x1*x2)+1/x1*x2好了,都转化成两根之和和两根之积了