`0,35xx16:0,28-(2,34+1,17:4,5):0,25`

`=5,6:0,28-(2,34+0,26):0,25`

`=20-2,6:0,25`

`=20-10,4=9,6`

a)Công suất hao phí:

\(P_{hp}=\dfrac{P^2\cdot R}{U^2}=I^2\cdot R=100^2\cdot0,2\cdot100=200000W\)

b)Muốn giảm \(P_{hp}\) đi 4 lần thì phải tăng \(U^2=4\Leftrightarrow U=2\) lần vì \(P_{hp}\) tỉ lệ nghịch với bình phương U.

1 D

2 A

3 B

II

1 B

2 A

III

1 N

2 D

3 D

4 C

5 A

6 C

7 D

8 A

9 B

10 A

IV

1 has been

2 invited

3 came - was cooking

4 to buy

Part B

1 C

2 D

3 B

4 C

5 C

II

1 It is a day that is meant to raise awareness and appreciation about the Earth's natural environment

2 In 1970

3 Yes, it did

4 C

5 There are more than one hundred and seventy five countries

Part C

1 Despite working hard, he can't support his large family

2 If you don't study harder, you will fail the final exam

3 My brother said that he wanted to go on holiday the day after

4 Most buildings in the city have been destroyed by the earthquake

5 We haven't seen her for 2 months

50 kW = 50,000W

4500kJ = 4 500 000 J

Thời gian chuyển động là

\(P=\dfrac{A}{t}\Rightarrow t=\dfrac{A}{P}=\dfrac{4,500,000}{50,000}=90\left(s\right)\) 

Lực kéo đầu tàu là

\(F=\dfrac{P}{v}=\dfrac{50,000}{10}=5000\left(N\right)\)

28 I haven't gone to HCM City for 2 years

29 We have lived in My Tho for ten years

30 Lan didn't go to school last week

31 He was at home yesterday

Question8:

29. We live in Phu Tho about ten years.

30. I will see him tomorrow.

31. Lan didn't go to school last week

32. He was at home yesterday.

Uh mình chỉ giúp được câu a

\(x^2-5x+3=0\)

\(\Delta=b^2-4ac\)

\(=\left(-5\right)^2-4.1.3\)

\(=25-12=13>0\)

\(x1=\dfrac{b+\sqrt{\Delta}}{2a}=\dfrac{5+\sqrt{13}}{2}\)

\(x2=\dfrac{b-\sqrt{\Delta}}{2a}=\dfrac{5-\sqrt{13}}{2}\)

25 What are you going to do this week?

26 We might go on holiday to the moon in the future

27 There will be a robot in my house

28 The room is very large

25.What are you going to do this week?

26.We might go on holiday to the moon in the future.

27.There will be have robot in my house.

28.The room is large

Chúc bạn học tốt✔✔