Tất cảToánVăn - Tiếng ViệtTiếng Anh
tíntiếnngân 7 giờ trước (21:41)Gọi m là độ dài một cạnh của hình vuông đó
aabb là diện tích của hình vuông đó(\(1000\le\overline{aabb}\le9999\))
ta có aabb = m2
=> 1100a + 11b = m2
=> 11(100a + b) = m2
suy ra \(m^2⋮11\Rightarrow m⋮11\left(tcm\right)\)
ta có aabb = m2
và \(1000\le\overline{aabb}\le9999\)
nên \(32\le m\le99\)
thử lần lượt với 33;44;55;66;77;88;99
ta có 88 thỏa mãn
vậy m = 88
Death Note 8 giờ trước (20:32)D = ( 2x - 1 )2 - 2 ( 2x - 3 )2 + 4
= 4x2 - 4x + 1 - 8x2 + 24x - 18 + 4
= ( 4x2 - 8x2 ) + ( 24x - 4x ) - ( 1 + 4 - 18 )
= -4x2 + 20x - 13
Ngô Gia Linh 8 giờ trước (20:48)\(D=\left(2x-1\right)^2-2\left(2x-3\right)^2+4\)
\(=4x^2-4x+1-8x^2+24x-18+4\)
\(=4x^2+20x-13\)
๖²⁴ʱ✰๖ۣۜCɦεɾɾү☠๖ۣۜBσмbʂ✰⁀ᶦᵈᵒᶫッ 8 giờ trước (20:49)Bài làm
\(D=\left(2x-1\right)^2-2\left(2x-3\right)^2+4\)
\(=-4x^2+20x-13\)
Vương Đức Hà 7 giờ trước (21:16)chùm hoa mới nở như một cô công chúa tí hon đẹp đẽ trào đời
cây đa tỏa bóng mát khắp sân trường
bạn mèo nhà em rất dễ thương
bố em là một bác sĩ
em rất ngoan
mùa hoa nở trên ngọn đồi vốn sác sơ , ko lá.
hok tốt
I. Cirlce the correct answer.
Question 1: When I last ________ him, he was living in London.
A. see B. have seen C. saw D. seen
Question 2: Who .......... food in your family when your Mom is away?
A. cooks B. is cooking C. has been cooking D. cooked
Question 3: The train ...............half an hour ago.
A. has been leaving B. left C. has left D. was leaving
Question 4: Jack ................... the door. It looks wet.
A. has just painted B. paint C. will have painted D. painting
Question 5: My sister ............... for you since yesterday.
A. is looking B. was looking C. has been looking D. looked
Question 6: I ................ Texas State University now.
A. am attending B. attend C. was attending D. attended
Question 7: He has worked in this factory..............................
A. ten years ago B. Since ten years C. for ten years ago D. for ten years
Question 8: Where is John? – He .............. his car in the garage.
A. repairs B. is repairing C. has repaired D. repaired
Question 9: I love this film. I .................... it four or five times already.
A. see B. have seen C. had seen D. will see
Question 10: Have you visited any European countries?
Yes. I .............. Spain and Italy two years ago.
A. visited B. have visited C. had visited D. will visit
Question 11: I ............to him when he comes back home.
A. will give B. give C. gave D. am giving
Question 12: My father .................for Mr. Smith for six years.
A. has worked B. will work
C. have been working D. is working
Question 13: Where is he? I ............... for him since three o'clock!
A. am waiting B. have been waiting C. was waiting D. had been waiting
Question 14: I can't leave now. I ................... for an important telephone call.
A. wait B. am waiting C. had been waiting D. was waiting
Question 15: I have waited for you ..................
A. since early morning B. since 9a.m C. for two hours D. All are correct
II. Fill in each blank with since or for.
III. Fill in each blank with since/for/ yet/ already
1 Things have changed a lot…………….our previous meeting.
2. It's been raining…………….four o'clock.
3. Have you done your homework ........................?
4. We've ....................... had dinner
5. I've been trying to fix this computer…………….early this morning.
6. He hasn't had anything to eat…………….nearly a week.
7. It's three years…………….he started learning German.
8. He's been collecting stamps…………….the past twenty years.
9. Nobody has seen him…………….last Friday.
10. It has been foggy…………….some days.
11. He hasn't finished his work .........................
12. They've been living in France …………….eight years.
13. The pilots have been on strike…………….two months.
14. We've had terrible weather…………….Saturday.
15. I've known Tom…………….1990.
16. We have been waiting for the bus…………….half an hour.
17. She hasn't lost a match…………….April.
18. Things have changed…………….she's become headmaster.
19. The police have been looking for him…………….a month.
20. Our dog has been ill…………….two days.
IV. Put the verbs into the present perfect tense.
1. The bill isn’t right. They (make)………….. a mistake.
2. Don’t you want to see this programme? It …………. (start).
3. I (turn)……….. the heating on. It’ll soon get warm in here.
4. ……..they (pay)…….. money for your mother yet?
5. Someone (take)………………. my bicycle.
6. Wait for few minutes, please! I (finish)……………. my dinner.
7. ………you ever (eat)………….. Sushi?
8. She (not/come)…………… here for a long time.
9. I (work)…………... here for three years.
10. ………… you ever …………..(be) in New York?
11. You (not/do) ………….yor project yet, I suppose.
12. I (just/ see)………. Andrew and he says he ……..already (do)………. about half of the plan.
13. I ………..just (decide)……… to start working next week.
14. He (be)…………. at his computer for seven hours.
15. She (not/have) ……………any fun a long time.
16. My father (not/ play)……….. any sport since last year.
17. I’d better have a shower. I (not/have)………. one since Thursday.
18. I don’t live with my family now and we (not/see)…………. each other for five years.
19. I…… just (realize)…………... that there are only four weeks to the end of term.
20. The train drivers (go)……… on strike and they stopped working at twelve o’clock.
V. The past simple or the present perfect?
1) The police....................two people early this morning. (arrest)
2) She …………….in this school since she ………………from university. (teach/ graduate)
3) Dan..................two tablets this year. (already/ buy)
4) How many games.................so far this season? (your team/ win)
5)................the CN Tower when you................in Toronto? (you/ visit - stay)
6)....................your homework yet? – Yes, I.................it an hour ago. (you/ do - finish)
7) There............an accident in High Street, so we have to use King Street to get to your school. (to be)
8) I...............Peter since I...............last Tuesday. (not/ see - arrive)
9) Frank..................his bike in May. So he...................it for 4 months. (get - have)
10) I'm sorry, I..................earlier, but I..................a lot lately. (not/ write - work)
11) Peter............... football yesterday (play)
12) They................. the car. It looks new again. (clean)
13) Last year we.................. to Italy. (be)
14) John and Peggy...................... the book. Now they can watch the film. (read)
15) I................. my friend two days ago. (meet)
16) We never…………….... another country before. (visit)
17) She......................... a new car in 2011. (buy)
18) I'm sorry, but I........................... my homework. (forget)
19)............you.................. the game of chess? (win)
20) The girls........................ their lunch yet. (eat)
VI. Rewrite the following sentences.
1.She has never drunk whisky before.
This is ....................................................................................
2.He has never seen this film before.
This is ....................................................................................
3.This is the first time we’ve visited Ha Long Bay.
We have .....................................................................................
4.The last time she visited me was 5 months ago.
She hasn't.....................................................................................
5. I last had my hair cut when I left her.
I haven't .....................................................................................
6.It is a long time since we last met.
We haven't.....................................................................................
TEST YOURSELF
I. Which underlined sound is pronounced differently in each group.
II. Give the right form of the following verbs :
III. Choose the best answer.
1. My brother plays volleyball very ........................
A. skillful B. skill C. skillfully D. skillfuly
2. Mai's sister speaks English ...................... than her.
A. fluently B. more fluent C. more fluently D. fluent
3. He is a ...................... driver. He has never had an accident.
A. careful B. carefully C. careless D. carelessly
4. Manchester is famous...............its football team.
A. in B. for C. at D. to
5. ................. do you live in? - Asia
A. Where B. What country C. What continent D. What city
6. ......................go to Tan Ky house? - Good idea.
A. What about B. Let's C. Why don't we D. How can we
7. Would you mind......................a hand?
A. give B. giving C. to give D. to giving
8. My sister works ......................... in my family.
A. hardest B. the most hardly C. hardly D. the hardest
9. The film was very .......................... I felt asleep in the middle.
A. scary B. boring C. exciting D. entertaining
10. Lan ..................some coffee for her father.
A. did B. made C. had D. gave
IV. Read and answer the questions.
John Logie Baird was born in Scotland in 1888. He became an inventor at the age of 26. His first inventions were electrically-heated socks and air-filled shoes, but these were not very successful. However, in 1923, he became interested in the idea of pictures by radio. He worked for several months and the following year he succeeded in transmitting the first “ television ” picture a few meters across the room.
Baird’s television was not very clear, but people were very interested in it and he tried to make it better. In 1926, he showed it to the public at the Royal Society. …
Questions:
1- Where was John Logie Baird born? ______________________________________
2- How old was he when he became an inventor? ______________________________________
3- Were his first inventions successful? ______________________________________
4- When did he show his invention to the public? ______________________________________
V. Make questions for the underlined part:
1. There are 40 students in my classroom.
2. My brother is studying in his bedroom.
3. My family usually goes to Da Lat on summer vacation.
4. Her children have watched TV for half an hour.
5. My favorite singer is David Archuleta.
6. The show lasts two hours and a half.
VI. Rewrite the sentences:
1. My father hasn’t gone fishing for a week
->The last time my father__________________________.
2. No place in the city is as historic as this one.
→ This place_________________________________________
3. I enjoy watching TV. (interested)
→ I am____________________________________________
4. My mom cooks better than my dad.
→ My dad_______________________________________
5. No one in my class dances as beautifully as Hoa.
-> Hoa _________________________________________
6. Her mother started cooking at four o’clock.
-> Her mother has __________________________________
7. Let's make some cakes.
-> How ________________________________
VII. Complete the following sentences.
1- He/ not/ clean/ bedroom/ yet.
2- How long/ they/ live here?
3- My father/ not/ be/ home yesterday/
4- Nam/ brother/ go/ fishing/ last weekend/.
5- You/ ever/ do judo/ before/?
6- I/ sometimes/ have/ Music/ Monday/.
7- This university/ famous/ than that/
Đọc tiếp...Câu hỏi tương tự Đọc thêm Báo cáo
kacura 29 tháng 11 2017 lúc 23:01giả sử aabb = \(n^2\)
<=>a . \(10^3\) + a .\(10^2\)+b.10+b = \(n^2\)
<=>11(100a+b)= \(n^2\)
=>\(n^2\) chia hết cho 11
=>n chia hết cho 11
do \(n^2\) có 4 chữ số nên
32 < n <100
=>n = 33 , n = 44 , n = 55 ,...n = 99
thử vào thì n = 88 là thỏa mãn
vậy số đó là 7744
Phạm Thị Phương Thảo 29 tháng 11 2017 lúc 22:58số đó là 7744
truong tien phuong 26 tháng 12 2016 lúc 18:24số đo diện tích là 7 chữ số tự nhiên 7 chữ số mà 2 chữ số đầu giống nhau; 2 chữ số cuối giống nhau là: 1234321.độ dài cạnh là:1111.
k mình nha bạn!
Ngoc Han ♪ CTV 8 giờ trước (20:21)\(1+\frac{1}{3}+\frac{1}{6}+\frac{1}{10}+\frac{1}{15}+\frac{1}{21}+\frac{1}{28}+\frac{1}{36}+\frac{1}{45}+\frac{1}{55}+\frac{1}{66}\)
\(=\frac{2}{2}+\frac{2}{6}+\frac{2}{12}+\frac{2}{20}+\frac{2}{30}+...+\frac{2}{90}+\frac{2}{110}+\frac{2}{132}\)
\(=2\times\left(\frac{1}{1\times2}+\frac{1}{2\times3}+\frac{1}{3\times4}+\frac{1}{4\times5}+\frac{1}{5\times6}+...+\frac{1}{9\times10}+\frac{1}{10\times11}+\frac{1}{11\times12}\right)\)
\(=2\times\left(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+...+\frac{1}{10}-\frac{1}{11}+\frac{1}{11}-\frac{1}{12}\right)\)
\(=2\times\left(1-\frac{1}{12}\right)\)
\(=2\times\frac{11}{12}\)
\(=\frac{11}{6}\)
๖²⁴ʱ✰๖ۣۜCɦεɾɾү☠๖ۣۜBσмbʂ✰⁀ᶦᵈᵒᶫッ 8 giờ trước (20:38)\(1+\frac{1}{3}+\frac{1}{6}+\frac{1}{10}+\frac{1}{15}+\frac{1}{21}+\frac{1}{28}+\frac{1}{36}+\frac{1}{45}+\frac{1}{55}+\frac{1}{66}\)
\(=\frac{2}{2}+\frac{2}{6}+\frac{2}{12}+\frac{2}{20}+\frac{2}{30}+...+\frac{2}{90}+\frac{2}{110}+\frac{2}{132}\)
\(=2\left(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}+\frac{1}{5.6}+...+\frac{1}{9.10}+\frac{1}{10.11}+\frac{1}{11.12}\right)\)
\(=2\left(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+...+\frac{1}{9}-\frac{1}{10}+\frac{1}{10}-\frac{1}{11}+\frac{1}{11}-\frac{1}{12}\right)\)
\(=2\left(1-\frac{1}{12}\right)=2.\frac{11}{12}=\frac{22}{12}=\frac{11}{6}\)
ĐănG 8 giờ trước (20:19)Bài làm:
Ta có: \(1+\frac{1}{3}+\frac{1}{6}+...+\frac{1}{66}\)
\(=\frac{1}{1}+\frac{1}{1.3}+\frac{1}{3.2}+...+\frac{1}{11.6}\)
\(=\frac{1}{2}\left(\frac{1}{1.2}+\frac{1}{2.1.3}+\frac{1}{2.3.2}+...+\frac{1}{2.11.6}\right)\)
\(=\frac{1}{2}\left(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{11.12}\right)\)
\(=\frac{1}{2}\left(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{11}-\frac{1}{12}\right)\)
\(=\frac{1}{2}\left(1-\frac{1}{12}\right)\)
\(=\frac{1}{2}.\frac{11}{12}\)
\(=\frac{11}{24}\)
Thắng Nguyễn CTV 12 tháng 9 2016 lúc 19:31\(Q=\frac{x^2}{\sqrt{x\left(x^3+8y^3\right)}}+\frac{2y^2}{\sqrt{y\left[y^3+\left(x+y\right)^3\right]}}\)
\(=\frac{x^2}{\sqrt{\left(x^2+2xy\right)\left(x^2-2xy+4y^2\right)}}+\frac{2y^2}{\sqrt{\left(xy+2y^2\right)\left(x^2+xy+y^2\right)}}\)
\(\ge\frac{2x^2}{2x^2+4y^2}+\frac{4y^2}{2y^2+\left(x+y\right)^2}\)\(\ge\frac{2x^2}{2x^2+4y^2}+\frac{4y^2}{2x^2+4y^2}=1\)
\(\Rightarrow Q\ge1\).Vậy MinQ=1
ミ★VĐ_TT^^★彡(Team NQCM) CTV 8 giờ trước (20:20)\(Q=\frac{x^2}{\sqrt{x^4+8xy^3}}+\frac{2y^2}{\sqrt{y\left(y^3+\left(x+y\right)^3\right)}}\)
Áp dụng bất đẳng thức Cauchy ta có:
\(x^4+8xy^3=x^4+8.xy.y^2\le x^4+4\left(x^2y^2+y^4\right)=\left(x^2+2y^2\right)^2\)
\(\Rightarrow\frac{x^2}{\sqrt{x^3+8xy^3}}\ge\frac{x^2}{x^2+2y^2}\)
\(\sqrt{y\left(y^3+\left(x+y\right)^3\right)}=\sqrt{\left(xy+2y^2\right)\left(x^2+y^2+xy\right)}\le\frac{x^2+3y^2+2xy}{2}=\frac{2y^2+\left(x+y\right)^2}{2}\)
\(\le\frac{2y^2+2\left(x^2+y^2\right)}{2}=x^2+2y^2\)
\(\Rightarrow Q\ge\frac{x^2}{x^2+2y^2}+\frac{2y^2}{x^2+2y^2}=1\)
Vậy minQ= 1 tại \(x=y>0\)
Hải Ngọc CTV 6 giờ trước (22:58)cách của mình cũng khá giống của Hermit nhưng chắc ngắn hơn
do x>0 nên ta co \(Q=\sqrt{\frac{x^3}{1+\frac{8y^3}{x^3}}}+\sqrt{\frac{4}{1+\left(\frac{x}{y}+1\right)^3}}\)
đặt t=\(\frac{y}{x}\)(t>0) thì ta có \(Q=\sqrt{\frac{1}{1+8t^3}}+\sqrt{\frac{4}{1+\left(\frac{1}{t}+1\right)^3}}\)
mặt khác theo bđt AM-GM ta có \(1+8t^3=\left(1+2t\right)\left(4t^2-2t+1\right)\le\frac{1}{4}\left(4t^2+2\right)^2=\left(2t^2+1\right)^2\)
\(\Rightarrow\sqrt{\frac{1}{1+8t^3}}\ge\frac{1}{2t^2+1}\left(1\right)\)
ta sẽ chứng minh \(\sqrt{\frac{4}{1+\left(\frac{1}{t}+1\right)^3}}\ge\frac{2t^2}{2t^2+1}\left(2\right)\)
thật vậy, ta có (2) \(\Leftrightarrow\left(2t^2+1\right)^2\ge t^4+t\left(t+1\right)^3\)
\(\Leftrightarrow\left(t-1\right)^2\left(2t^2+t+1\right)\ge0\)(luôn đúng)
từ (1) và (2) ta suy ra \(P\ge\frac{1}{2t^2+1}+\frac{2t^2}{2t^2+1}=1\)
đẳng thức xảy ra khi \(\hept{\begin{cases}1+2t=4t^2-2t+1\\t=1\end{cases}\Leftrightarrow t=1\Leftrightarrow x=y}\)
tíntiếnngân 7 giờ trước (21:51)Xét \(\Delta BDC\)và \(\Delta EBC\)
ta có \(\widehat{BDC}=\widehat{EBC}\)(cùng phụ với \(\widehat{BED}\))
\(\widehat{DCB}=\widehat{BCE}=90^0\)
nên \(\Delta BDC\)đông dạng \(\Delta EBC\)(g-g)
dễ chứng minh \(\Delta BCD\approx\Delta EBD\left(g-g\right)\)
nên \(\frac{BD}{DE}=\frac{CD}{BD}\Rightarrow BD^2=CD\cdot DE\)
Trên đường thẳng xx' lấy điểm O tùy ý. trên cùng một nửa mặt phẳng bờ là đường thẳng xx' vẽ 2 tia Oy và Oz sao cho góc xOz = 30 độ. Góc x'oy= 4. xOz
a) Trong 3 tia Ox, Oy, Oz tia nào nằm giữa 2 tia còn lại ?
b) Chứng tỏ rằng Oz là tia pgiác của góc xOy
c) Gọi Oz là tia phân giác của góc x'Oy tính góc zOz'
Đọc tiếp...Được cập nhật 8 giờ trước (20:08)
Câu hỏi tương tự Đọc thêm Báo cáo
ngo thi diem 3 tháng 8 2016 lúc 9:53a) tia Oz nam giua tia Ox va Oy
b) góc x'Oy =4*xOz =4* 30=120
ta co xOz +zOy + yOx'= 180 (x O x' thang hang)
30 +xOy +120=180 => zOy =30 ma xOz =30 => xOz= zOy Oz nam giua 2 tia Ox va Oy => Oz la phan giac cua xOy
c) Oz' la phan giac cua yOx' => yOz = \(\frac{yOx'}{2}=\frac{120}{2}=60\)
zOz'= zOy+yOz =30+60=90
Dưới đây là những câu hỏi có bài toán hay do Online Math lựa chọn.
