Ta có

3C = 3+3² + 3³ +...+3¹¹ + 3¹²

=> 3C - C = 2C = 3+3² + 3³ +...+3¹¹ + 3¹² - (1+3+3² + 3³ +...+3¹¹)

                       = 3¹² - 1

=> C = (3¹² - 1)/2 = 265720

=> C chia hết cho 40 (vì 265720:40 = 6643)

What is.....the distance between your school and the cinema?.

She doesn't have any friends in HCM city

She has.....no friend in hcm city.

Jacky likes football best

Football....is jacky's favorite sport.

She never late for school

She always.....go to school early.

The B-store is on the left of my school anh the Vin Mart is in the right of my school

My school.....is between the b-store and the vin mart

My school library (1) .............is............. very big. It is (2) .......on..................... the right of the lab. Every day, a lot of students come there to read books and magazines. There (3) ...........are................ hundreds of book of all kinds. English books are (4) ....on................... the shelves (5) .....to................ the right. Those shelves on the left (6) ...........have................ science books : chemistry, (7) ......physics.................., and biology. In the (8) ........middle................ of the library, there are two racks (9) ..........contain..................... magazines and newspapers. We like reading all the books there (10) ..........beacause..................... they are very interesting and useful.

1.He was annoyed because I walked across the field.

=> He ojected to my walking across the field.

2. I am fond of my nephew although he behaves terribly.

=> I am fond of my nephew in spite of his terrible behavior.

3. I won't swim in the sea because it is too cold.

=>The sea is not warm enough for me to swim

4." I was not there at the time " he said

=> He denied being there at time.

5. " Who does that suitcase belong to " the policeman asked us

=> The policeman asked us whoes suicase it was

6. she hasn't ridden a horse before.

=>It is the first time, she has ridden a hourse

7. Haven't you got any cheaper televisons.?

=> Are these your cheapest television?

8.The children should be in bed by now.

=> It's time for the children to be in bed.

9.He can't do anything about it. 

=>There's nothing he can do about it

10. He borrow my book , but he forgot to return it.

=> I lent him my book, but he forgot to return it

câu1 : cần sửa lại là A²  + B² \(\ge\frac{1}{2}\)

Ta chứng minh được : (A+B)² \(\le2.\left(A^2+B^2\right)\) (*)

<=> A²  + B²  + 2A.B \(\le\) 2. (A²  + B²)

<=> 0 \(\le\) A²  + B²  - 2.A.B <=> 0 \(\le\) (A-B)² luôn đúng => (*) đúng

b) Áp sung câu a => (x+y)² \(\le\)2.(x² + y²) = 2 => đpcm

8.our leson are written in lass .

 MK BỔ SUNG THÊM

1, Miss Lan teaches English

English is teached by miss lan.

2, Her sister often makes coffee

coffee is often made by her sister.

3, the librarian helps us

we are helped by the librarian.

4, His father sometimes takes him to the zoo

he is sometimes took to the zoo by his father.

5, My father bought a new car last year

a new car was bought by my father last year.

6, The principal doesnot write this letter

this letter isn't written by the principal.

7, Does she clean the floor yesterday ?

was the floor cleaned yesterday?

8, We write our leson in lass

121.I saw  a light in your house as I (pass) ………passed………..

122.I (not eat) ………didn't eat…….. anything yesterday because I (not feel) …didn't feel………….. hungry.

123.What …were…… you (do) …doing……… when I (see) ……saw…… you ?      - I was on my way home.

124.Don’t worry. I (give) ……will give….. you a lift. I am sure you’ll be at the station in 10 minutes. 

125.Could you be quiet, please ?    - I ( listen) ………am listening………….. to the radio.

126.The children are late. They (not come) ……haven't came………….home from school yet. I hope nothing’s wrong.

127.I decided not to go out because it (rain) ……was rained…………

128.Look! You (make)……are making……….. the same mistake again.

- Oh, no. Not again I always ( make) …………make………that mistake.

128.Let me look at you. You (not change) ……haven't changed……..……much since I met you.

130.I (tell) ……wiil tell…….. you about it when I have time.

131.If you don’t get up early, you (be) ……will be……… late for school.

132.Would you like to go to the cinema tonight ?       - Yes, please. When …wiil…. we (meet) ……meet…… ? 

133.Why do you have a pencil in your hand ?       - I (draw) ..…………draw……………. a cartoon.

134.What do you want to be when you grow up ?    - I (be) …..………am…………. a teacher.

135.Ann (want) ……wants…….. to see you. You (not see) ………haven't seen………… her for a long time.

136.Do you know where he lives ?    - No, he recently (move) ……moves………. to a new flat. I (not be)....am not.....     

137.They (be) ………were…….. there nine months ago.                                                                     there yet.

138”…do….. you (know) ……know…….Eliza?”     “ Yes”.   “ How long ……do… you (know) ……know…..her ?”

139.Mrs Smith (work) ……has worked…. in the library since 1983

140.I’ve been in this city for a long time. I (come) ……came……… .. here sixteen years ago.

141.Hurry up! We’re waiting for you. What’s taking you so long ?

- I (wait) ………am waiting……… for an important phone call. Go ahead and leave without me.

142.Robert is going to be a famous someday. He (appear) ……has appeared………….in three movies already.

143.Why did you buy all this sugar and chocolate ?  

- I (make) …………will make………………...a delicious dessert for dinner tonight.

146.The earth (depend)(phụ thuộc) ………depends……….on the sun for its heat and light.

147.Ahhhh ! I (try) ………am trying………….. to concentrate(tập trung). I can’t hear myself think with all that noise going on.

148.Mrs Lien is at the market. Right now she (look) ……is looking………. at the apples. They (look) …look…fresh.

149.Nam (not hear) ………didn't hear………...his parents having a argument last night. He (listen) ……listens………… to music in his room.

150.When I was a child, my mother always (serve) ……served………..cookies and milk to my friends and me

when we (go) ……went……..to my after school.

151.Jane is expecting (mong đợi)a letter from me, but I (not write) ………haven't………………. to her yet. 

152.Let’s stop at the next motel. We (drive) …………drive………. 500 miles so far today and that’s enough.

153.Everyone makes mistakes in life. I ( make) …………make……………. lots of mistakes in my life. The important thing is to learn from one’s mistakes. Right ?

154.I understand Tom is a good friend of yours ?   - How long …have….. you (know) …known…….. him ?

- Since we (be) …………were………kids.

155.My wife and I (move) ………have moved……….. three times since we (get) ……got……. married.

156.I knew Tim when he was a child, but I (not see) ……haven't seen……….. him for many years.

157.Nga missed her English examination this morning because she (oversleep)………have overslept…………… She  (oversleep)……have overslept………….. a lot since the beginning of the semester. She’d better buy a new alarm clock

158.Jạc really needs to get I touch with you. Since this morning, he (call) …..…has called…………here four times trying to reach you. He (call) ……called……...at 9:10, 10:25, 12:15 and 1:45

159.Alex is an artist. He (draw) ……draws………. many beautiful pictures in his lifetime. Last week, he (draw) 

…………drew………a beautiful mountain scene.

160.The world (enjoy) ………has enjoyed………... Beethoven’s music for nearly 200 years.

161. Since they (learn) ………learned……..that cigarettes cause cancer, many people have stopped smoking.

162.I’ve come out without  any money.- Never mind. I (lend) ……wiil lend… you some. How much do you want ?

163.I am catching the 6:30 train.                     - So am I. I (give) ……give………….. you a lift to the station.

164.Look at those black clouds. It (rain) ………is raining………..

165.The old man (fall) ………fell……. as he (get) ………got………. into the bus yesterday.

166.The earth (move) ……moves……….. around the sun.  167. Something (smell) …..are smelling……good in the kitchen now.

168.I (tidy) ……tidy………..my desk, but now it’s in a mess again.(bề bộn, lộn xộn)

169.The last time I (go) ……went………to Brighton was in August.