1/x1+1/x2=(x2+x1)/x1*x2
a=2 b=4 c=-3
根据韦达定x1+x2=-b/a=-2 x1*x2=c/a=-3/2
所以1/x1+1/x2=(x2+x1)/x1*x2=(-2)/(-3/2)=4/3