有两个实数根
判别式(2m+3)^2-4m^2>=0
12m+9>=0
m>=-3/4
x1+x2=2m+3
x1*x2=m^2
1/x1+1/x2=(x1+x2)/x1x2=(2m+3)/m^2=1
m^2=2m+3
m^2-2m-3=0
(m-3)(m+1)=0
因为m>=-3/4
所以m=3