50. Someone had invented electric lights before I was born. ……………………………………………………………………………………………………. 51. Before they took exams they had revised their lessons. …………………………………………………………………………………………………… 52. When he came home his father was reading a newspaper. …………………………………………………………………………………………………… 53. My father will take me to Ho Chi Minh City next week. ………………………………………………………………………………………………….. 54. When I was 18 years old, my parents allowed me to go out in the evening. …………………………………………………………………………………………………… 55. You were wearing your new hat when I met you yesterday. …………………………………………………………………………………………………… 56. He is preparing everything for the presidential election. …………………………………………………………………………………………………… 57. Last Friday, when I came to Jane’s house, she had finished all exercises. …………………………………………………………………………………………………… 58. Countries are finding a way to solve the problem. …………………………………………………………………………………………………… 59. He put the letter in the drawer, and then he locked it up. …………………………………………………………………………………………………… 60. By the end of this year, we will have learnt 2,000 English words. …………………………………………………………………………………………………… 61. Her father was planting different kinds of flowers in the garden. …………………………………………………………………………………………………… 62. The Prime Minister is making a speech at the moment. …………………………………………………………………………………………………… 63. The doctor pulled out one of my teeth yesterday morning. …………………………………………………………………………………………………… 64. His wife usually brings him sandwiches at lunch time. …………………………………………………………………………………………………… 65. The light went out while I was making a cup of tea. …………………………………………………………………………………………………… 66. When she went to Barcelona, she learnt some Spanish. …………………………………………………………………………………………………… 67. The students of chemistry made many experiments last week. …………………………………………………………………………………………………… 68. For the past years, I have done all my washing by hand. ……………………………………………………………………………………………………

MN ƠI AI GIÚP MIK VỚI Ạ Hai pha dao động điều hòa cùng phương cùng tần số, dao động thứ nhất có biên độ A1=6cm, pha ban đầu pi/6 và dao động thứ hai có biên độ A2 pha ban đầu 5pi/6. Biên độ A2 thay đổi được. Biên độ dao động tổng hợp A có giá trị nhỏ nhất là bao nhiêu

Chứng minh rằng 1/ (sin x + cos x)^2 = 1+2sin x . cos x 2/ sin^4x + cos^4x = 1-2sin^2x . cos^2x 3/ sin^6x + cos^6x = 1-3sin^2x . cos^2x 4/ 1-sinx / cos x = cos x / 1+sin x giúp mình với nhaaaa

complex sentences from cach pair of sentences. Use the subordinator prov and make any necessary changes. 1. It might rain. Take an umbrella with you. (in case) 8. They were reading. Their mother was watching TV. (while) 9. He had checked every door. He went out today. (before)

Passive voice with two objects 1. Rachel will give you some advice. You ..................................................................................................................................................... Some advice ....................................................................................................................................... 2. I sent him a letter. ............................................................................................................................................................ ............................................................................................................................................................ 3. The police officer showed us the way. ............................................................................................................................................................ ............................................................................................................................................................ 4. Our neighbor gave me a lift. ............................................................................................................................................................ ............................................................................................................................................................ 5. She told me a lie. ............................................................................................................................................................ ............................................................................................................................................................ 6. They have written her a postcard. ............................................................................................................................................................ ............................................................................................................................................................ 7. Kerrie will make you a cup of tea. ............................................................................................................................................................ ............................................................................................................................................................ 8. The waiter has not brought us the coffee. ............................................................................................................................................................ ............................................................................................................................................................ 9. They did not offer her a seat. ............................................................................................................................................................ ............................................................................................................................................................ 10. We bought Betty a bit of butter. ............................................................................................................................................................ ............................................................................................................................................................

Mọi người giúp em câu này với ạ ! 2sin$^{3}$ ( x + $\frac{\pi}{2}$ ) + cos2x + cos ( $\frac{9\pi}{2}$ - x ) = 0

Hòa tan hết 4,6g Na vào cốc chứa 245,6g H2O thu được dd X Tính nồng độ mol và nồng độ % của dd X Biết Dx=1,25g/ml

cho $a+b\leq 1$. Tìm gtnn của $ab+\frac{1}{ab}$

Btvn¹: Tính bằng cách thuận tiện ($\frac{27}{25}$ - $\frac{4}{9}$) - ($\frac{2}{25}$ - $\frac{5}{9}$)

cho f{x}=x mũ 2- mx+15 a} tìm m để f{x}nhân 3 là 1 nghiệm b với vừa tìm được hãy tìm nghiệm còn lại của f {x}