设:r1=AC r2=BC
因为是平行向左的.
又因为角B=30
所以
Ea/Eb=1/2
又因为E=kQ/r^2
所以Qa/Qb=(r1^2*Ea)/(Eb*r2^2)=(Ea/Eb)*(r1^2/r2^2)=(1/2)*(1/4)=1/8