x1+x2=4/3,x1x2=-1/3
(1)(x1-2)(x2-2)=x1x2-2(x1+x2)+4=-1/3-8/3+4=1
(2)x1-x2=根号((x1+x2)^2-4x1x2)=根号(16/9+4/3)=三分之两倍的根号7
(3)（x1÷x2)+(x2÷x1）=(x1^2+x2^2)/x1x2=[(x1+x2)^2-2x1x2]/x1x2把数字带进去算就可以了