由P=UI,I= U R 得,P= U2 R ,电阻R1、R2并联时,两电阻功率之比 P1 P2 = U1 R1 U2 R2 = R2 R1 = 4 3 ,所以 R1 R2 = 3 4 ;由P=UI,I= U R 得,P=I2R,电阻R1、R2串联时,两电阻功率之比 P P = I2R1 I2R2 = R1 R2 = 3 4 .故答案为:3:4.