最小波长设为λ，最大波长设为λ’，hc/λ=-13.6eV(-1/2²)hc/λ'=-13.6eV(1/3²-1/2²)所以：λ/λ'=(1/2²-1/3²)/(1/2²)=(3²-2²)/3²=5/9
