1. was waiting - came

2. rang - was watching

3. began - was sitting

4. was having - arrived

5. was listening - was reading

6. had - was repaired

7. was taking - went

8. was looking - found

9. was watching - rang

10. were - doing

Vôn kế mắc song song với R1 có tác dụng đo HĐT R1

=> HĐT giữa 2 đầu R1 là U1

Vôn kế mắc song song với R2 có tác dụng đo HĐT R

=> HĐT giữa 2 đầu R2 là U2

R1 nt R2 <=> I1=I2 (1)

Mà theo định luật Ôm:

I1=\(\dfrac{U1}{R1}\) ; I2=\(\dfrac{U2}{R2}\) (2)

Từ (1) và (2) ta có: \(\dfrac{U1}{R1}\) = \(\dfrac{U2}{R2}\)

<=> \(\dfrac{U1}{U2}\) = \(\dfrac{R1}{R2}\)

b,