Áp dụng tính chất của dãy tỉ số bằng nhau:
\(\frac{1111c-99d}{9999c-11d}=\frac{1111a-99b}{9999a-11b}=\frac{1111c-99b}{9999c-11b}=\frac{1111a-99d}{9999a-11d}\)
\(\Rightarrow\frac{1111c-99d}{9999c-11d}=\frac{1111a-99b}{9999a-11b}\left(đpcm\right)\)
Vậy ....
cho \(\frac{a}{b}=\frac{c}{d}\)
Chứng minh rằng : \(\frac{a}{b+c}=\frac{b}{2b+d}\)
tìm các số a,b,c biết 2a=\(\frac{3b}{2}\)=\(\frac{4}{3}c\)và a-2b+3c=34
Cho tam giác ABC cân tại A. Trên tia đối tia BA và CA lấy lần lượt hai điểm M và N sao cho BM=CN. Gọi I là giao điểm của MC và BN
a/ Chứng minh rằng: MI=MN
b/ Tia phân giác của góc AMC cắt AI tại O. Chứng minh rằng: MO>\(\frac{MC}{2}\)
\(\frac{5}{2}-\frac{1}{3}+\frac{1}{4}\)
\(\frac{2}{5}-0,4+3\frac{1}{2}\)
\(\left(\frac{3}{4}-4\right):\left(\frac{1}{2}+\frac{1}{8}\right)\)
\(\frac{7}{13}:\frac{8}{17}+\frac{7}{13}\cdot\frac{5}{17}\)
\(\frac{1}{3\cdot5}+\frac{1}{5\cdot7}............+\frac{1}{91\cdot93}\)
Với những giá trị nào của x thì
\(\frac{2}{3}-\frac{7}{2}x\div\frac{x}{5}+1\frac{7}{11}\)
tìm x, y biết \(\frac{x^2+y^2}{10}=\frac{x^2-2y^2}{7}\) và \(x^4.y^4=81\)
\(\frac{3}{7}-\frac{4}{7}:\left(x-1\right)=\frac{-5}{7}\)
giải hộ mình nha
1. When ____________ the school?
A) have you joined B) did you joined C) did you join D) have you ever joined
2. _____________ in England? A) Did you ever worked B) Have you ever worked C) Worked you 11D) Didn't you have worked
3. That's the best speech _________
A) I never heard B) I didn't hear C) I used to hear D) I've ever heard
4. He's the most difficult housemate _____________________A) I never dealt with. B) I never had to deal with. C) I've ever had to deal with. D) I've never had to deal with
5. ______ to him last week.
A) I spoke B) I've already spoken C) I didn't spoke D) I speaked
6. _____a contract last year and it is still valid.
A) We have signed B) We signed C) We haven't signed D) We have sign
7. ______ from a business trip to France.
A) I come back B) I came back C) I never came back D) I've just come back
8. Prices ________ in 1995 but then _____ in 1996.
A) rised _ falled B) rose _ fell C) have risen _ have fallen D) rose _ have fallen
9. You ____________ to a word ____________A) listened _ I haven't said
B) didn't listen _ I say C) listened _ saying D) haven't listened _ I've said back
10. I can't believe that ________________ the news.A) you haven't read
B) you didn't read C) you don't read D) you read not.
11.You ……………… a lot since the last time I saw you.
A. changed B. has changed C. is changing D. have changed
12. He………. more concerned about his social status since he started working there.
A. has been becoming B. has become C. became D. will become
13. Travel ………… into a huge industry in the last few decades.
A. has turned B. is turning C. has been turning D. have turned
14. Science …………. in leaps and bounds.
A. have advanced B. has advanced C. has been advanced D. is advancing
Man ……………… great things.
A.is accomplished B. has been accomplishing
C. has accomplished D. have accomplished
15. I ……………. the report yet.
A. hasn’t completed B. completed
C. have already completed D. have not completed
16. The rain ……………….. . It’s been raining for 3 hours.
A. has stop B. is stopped C. haven’t stopped D. hasn’t stopped
17. They ……………… at the airport.
A. haven’t yet arrived B. haven’t already arrived
C. hasn’t yet arrived D. didn’t arrive
18. We ………………. three power cuts this week.
A. has had B. have had C. had D. is having
19. The team ……………. numerous setbacks so far.
A. experienced B. have experience C. has experienced D. is experiencing
20. John ……………. for three tests this month.
A. sat B. have sat C. has sat D. is sitting
21………… you …………. abroad this year?
A. Has – been B. Has – gone C. Have – be D. Have – been
22. I …………….. three books by the same author since the last month.
A. has read B. have read C. read D. red
23. Kathy …………….. for three different companies since graduating two years ago.
A. has worked B. have worked C. have been worked D. worked
24. This is the first time I ………….. to Germany.
A. has ever been B. have been ever C. has been ever D. have ever been
25. He ………….. to France for ages.
A. has gone never B. have never gone C. has never gone D. never has gone
26. They ……………. skiing since they were 15.
A. have never gone B. has gone never C. has never gone D. have gone never
27. I …………….. a cold for two weeks.
A. has had B. have had C. had D. have been had
28. He ………… here for six months.
A. have been B. has been being C. has been being D. has been
29. My friend and I …………… for too long.
A. has been waited B. has waited C. have waited D. have been waited
30. I…………….. Martha.
A. ‘s just seen B. ‘ve just seen C. ‘ve seen just D. ‘s seen just
31. He ………………….. to her over the phone.
A. has only spoken B. have spoken only
C. have only spoken D. has spoken only
32. Did you like the new Doctor Who season? – I …………… it yet.
A. hasn’t seen B. has seen C. have seen D. haven’t seen
33. George is a very close friend of mine. We …………… each other for years.
A. knew B. have known C. has know D. had knew
34. You’ve … for work too many times this year. If you’re not careful, you’ll be fired.
A, ‘ve been late B. ‘s been late C. ‘ve be late D. ‘s be late
tìm x
\(\frac{2.x-1}{3x}< 0\)
