设电源电压为U,在时间t内电阻产生的热量:Q1=I12R1t=( U R+R1 )2R1t,Q2=I22R2t=( U R+R2 )2R2t,由题意知Q1=Q2,即( U R+R1 )2R1t=( U R+R2 )2R2t,解得: R1R2 =R.故答案为: R1R2 =R.