a) + Vẽ đương pháp tuyến IN vuông góc với gương tại I

+ Vẽ tia phản xạ IR sao cho góc NIR = góc SIN

b) + Tính góc tới SIN:

góc \(SIN=90^0-30^0=60^0\)

_ Góc phản xạ NIR

Theo định luật phản xạ ánh sáng ta có góc tới bằng góc phản xạ nên;

\(\Rightarrow NIR=SIN=60^0\)

TÌM LỖI SAI VÀ SỬA

1.He is good at speaking. He practices to English every day

=>∅

2. The river is the same long as that one

=>length

3. This is the most interesting film I have ever see

=>seen

4. The rooms looks beautifully when did you paint it?

=>beautiful

5. Everyone have his own dreams about his future

=>has

6. I feel very pride to be a part of this football team

=>proud

7. They do morning exercise so as improve their health

=>∅

8. Could you help me how solve this problem?

=>to solve

25x=42.25+25.37

25x=25.(42+37)

25x=25.79

25x=1975

    x=1975:25

    x=79

Đặt \(\dfrac{a+b}{3}=\dfrac{b+c}{4}=\dfrac{c+a}{5}=k\)

\(\Rightarrow\left\{{}\begin{matrix}a+b=3k\\b+c=4k\\c+a=5k\end{matrix}\right.\Rightarrow2\cdot\left(a+b+c\right)=12k\Rightarrow a+b+c=6k\)

\(\Rightarrow\left\{{}\begin{matrix}c=3k\left(1\right)\\a=2k\left(2\right)\\b=k\left(3\right)\end{matrix}\right.\)

Thay \(\left(1\right),\left(2\right),\left(3\right)\) vào BT ta có:

\(M=10\cdot2k+k-7\cdot3k+2017\)

\(M=20k+k-21k+2017\)

\(M=21k-21k+2017\)

\(M=2017\)

Vậy \(M=2017\)

47 - 5(10 - x) = 12

5(10 - x) = 47 - 12

5(10-x) = 35

10 - x = 35 : 5

10 - x = 7

x = 10 - 7

x = 3

Bạn tick cho mình nhé!!!

Gọi số sản phẩm mỗi người làm được lần lượt là x, y, z ( đơn vị: sản phẩm, x , y , z >0 )

Trong cùng 1 thời gian thì số sản phẩm làm được và thời gian là 2 đại lượng tỉ lệ nghịch nên theo bài ra ta có :

\(\left\{{}\begin{matrix}x\cdot10=y\cdot12=z\cdot18\left(1\right)\\x+y+z=215\end{matrix}\right.\)

Từ (1) \(\Rightarrow\dfrac{x}{\dfrac{1}{10}}=\dfrac{y}{\dfrac{1}{12}}=\dfrac{z}{\dfrac{1}{18}}=\dfrac{x+y+z}{\dfrac{1}{10}+\dfrac{1}{12}+\dfrac{1}{18}}=\dfrac{215}{\dfrac{43}{180}}=900\)

\(\Rightarrow x=900\cdot\dfrac{1}{10}=90\left(TMĐK\right)\)

\(\Rightarrow y=900\cdot\dfrac{1}{12}=75\left(TMĐK\right)\)

\(\Rightarrow z=900\cdot\dfrac{1}{18}=50\left(TMĐK\right)\)

Vậy người t1 làm được là 90 sản phẩm

người t2 làm được là 75 sản phẩm

người t3 làm được là 50 sản phẩm

Gọi số HS gỏi, khá, trung bình của lp 7A lần lượt là x,y,z ( đơn vị; em, x ,y ,z > 0 )

Theo bài ra ta có:\(\dfrac{x}{1}=\dfrac{y}{2}=\dfrac{z}{3}=\dfrac{x+y+z}{1+2+3}=\dfrac{36}{6}=6\) ( t/c của dãy tỉ số bằng nhau)

\(\Rightarrow\dfrac{x}{1}=6\Rightarrow x=6\left(TMĐK\right)\)

\(\Rightarrow\dfrac{y}{2}=6\Rightarrow y=12\left(TMĐK\right)\)

\(\Rightarrow\dfrac{z}{3}=6\Rightarrow z=18\left(TMĐK\right)\)

Vậy số HS giỏi lớp 7A là 6 em

số Hs khá lớp 7A là 12 em

số HS trung bình lớp 7A là 18 em

EXERCISE 1: Use the correct form of verbs in brackets.

1. In all the world, there (be) ____are______ only 14 mountains that (reach) ____reach______above 8,000 meters.

2. He sometimes (come) ____comes______ to see his parents.

3. When I (come) ____came______, she (leave) ___had left_______for Dalat ten minutes ago.

4. My grandfather___have__ never (fly) ______flown____ in an airplane, and he has no intention of ever doing so.

5. We __have___just (decide) ____decided______ that we (undertake) ______would undertake______ the job.

6. He told me that he (take) ___would take_______ a trip to California the following week.

7. I knew that this road (be) ___will be_______ too narrow.

8. Right now I (attend) ___attending_______ class. Yesterday at this time I (attend) _____was attending_____class.

9. Tomorrow I'm going to leave for home. When I (arrive) ____arrive______at the airport, Mary (wait) ___will be waiting_______ for me.

10. Margaret was born in 1950. By last year, she (live) ___has lived_______on this earth for 55 years

11. The traffic was very heavy. By the time I (get) _____got_____to Mary's party, everyone (arrive) ____had already arrived______

12. I will graduate in June. I (see) ____will see______ you in July. By the time I (see) _____see_____ you , I (graduate) ____will have graduated______.

13. I (visit) _____visited_____ my uncle's home regularly when I (be) ____was______ a child.

14. That book (be) _____has been_____ on the table for weeks. ______Haven't____ you (not read) ____read______ it yet ?

15. David (wash) ____is washing______ his hands. He______has____ just (repair) ___repaired_______ the TV set.

16. ______Have____ you (be) ____been______here before? Yes, I (spend) _____spent_____ my holidays here last year.

17. We ______have____ never (meet) ___met_______ him. We don't know what he (look) ________looks__ like.

18. The car (be) ___will have been______ ready for him by the time he (come) ___comes_______tomorrow.

19. On arriving at home I (find) ____found______that she_____has_____ just (leave) _____left_____a few minutes before.

20. When we (arrive) ______arrive____ in London tonight, it______will____ probably (rain) ____be raining_____.

21. It (rain) ___is raining_______ hard. We can't do anything until it (stop) ___stops_______

22. Last night we (watch) ____were watching______TV when the power (fail) ____failed______.

23. That evening we (stay) _____stayed_____up to talk about the town where he (live) ____has lived______for some years.

24. I (sit) _____sat_____down for a rest while the shoes (repair) ____were being repaired______.

25. Half way to the office Paul (turn) ____turned______round and (go) ____went______back home because he (forget) ___had forgotten_______to turn the gas off.

26. London (change) ____has changed______a lot since we first (come) _____came_____ to live here.

27. While we (talk) ____were talking ______on the phone the children (start) _____started_____fighting and (break) ___broke_______a window

28. He used to talk to us for hours about all the interesting things he (do) ______had done____ in his life.

29. You know she (stand) _____has been standing_____looking at that picture for the last twenty minutes.

30. I (spend) ____has spent______ a lot of time travelling since I (get) __got________this new job.

31. When we (be) ____were______ at school we all (study) _____studied_____Latin.

32. When I (meet) ______met____ him , he (work) ______had been working____as a waiter for a year.

33. After he (finish) _____had finished_____ breakfast he (sit) _____sat_____down to write some letters.

34. She (have) ____has______a hard life, but she's always smiling.

35. I think Jim (be) _____will be_____ out of town.