Cho góc xOy lấy điểm A thuộc tia Ox , điểm B thuốc tia Oy sao cho OA =OB đường đường vuông góc với Ox tại A, đường vuông góc với Oy tại B cắt nhau tại C .Cmr: OC là tia phân giác của góc xOy vẽ hình nữa ạ

Xét dấu biểu thức sau A=(x^2 -2x- 1/2)^2-(2x-7/2)^2 GIÚP MÌNH VỚI

Cho ∆ABC vuông tại A. Kẻ AH vuông góc BC.a) Chứng minh : AB²+CH²=AC²+BH².b)Trên AB lấy E. Trên AC lấy điểm F. Chứng minh: EF<BC. c) Biết AB =6cm .AC= 8cm . Tính AH , BH, ơiCH giúp vs mn

1,Tìm x thuộc Z: (x+3).(y+1)-1=2. 2,Tìm x ,biết :2|x-5|-3=5

biết số học sinh của một trường trong khoảng 700 đến 800 học sinh, khi xếp hàng 30, 36, 40 đều thừa 10 học sinh. tính số học sinh của trường đó

Cho a+5b chia hết cho 7 (a,b ∈N), Chứng minh rằng 10ab chia hết cho 7. Mệnh đề đảo lại đk?

SECOND CONDITIONALS EXERCISES. Complete the following sentences with the words in brackets. 1. What would you do if you suddenly (win) _______________ half a million pounds? 2. If he (get up) _______________ up earlier, he'd get to work on time. 3. If we (have) _______________ more time, I could tell you more about it. 4. If you (sell) _______________ more products, you'd earn more money. 5. I could help you if you (trust) _______________ me more. 6. I'd come to your party if I (finish) _______________ my project. 7. I wouldn't be able to do it unless you _______________ (help) me. 8. If it got dark we (not find) _______________ the way. 9. I'd sit down here if you (not mind) _______________. 10. If you turned up the radio we (hear) _______________ the news. 11. If the weather was nice I _______________ (go) out with you. 12. I would tell you the truth if you (not laugh) _______________at me. 13. How much would it cost if we (pay) _______________ in advance? 14. He (cannot go) _______________ to the States unless he asked for a visa. 15. What would you do if you (lose) _______________ your passport? 16. If I missed the bus, (you – take) _______________ me by car? 17. He wouldn't agree with it if it (not be) _______________ fair. 18. His car would be a lot safer if he (buy) _______________ some new tires. 19. The children could be better swimmers if the (go) _______________ swimming more frequently. 20. I wouldn't mind having children if we (live) _______________in the country. 21. If I (be) _______________ you, I wouldn't worry about going to university. 22. If I (have) _______________ any money, I'd give you some. 23. Your parents (be) _______________ a lot happier if you phoned them more often. 24. I (write) _______________ to her if I knew her address. 25. I wouldn’t mind living in this country if the traffic (not/be) _______________ so bad. 26. If I showed you how to open the safe, (you/promise) _______________ not to tell anyone? 27. If the police come looking for you I (say) _______________ you have left the country. 28. If you (move) _______________ to the UK you would have to learn to speak English. 29. She (not/buy) _______________ it if she didn’t think she needed it. 30. The salad (taste) _______________ better if you added some garlic. 31. We (grow) _______________ our own vegetables if we had a garden. 32. What will you do if the boat (sink) _______________ . 33. When the sun (shine) _______________ I like to lie on the beach. 34. If I _______________ (have) a yacht, I would sail around the world. 35. If David _______________ (be) taller, he could even play in NBA.

Cho a,b,c>0 thỏa mãn `ab+bc+ca=3` CMR: `root{3}{a/(b(b+2c))}+root{3}{b/(c(c+2a))}+root{3}{c/(a(a+2b))}>=3/(root{3}{3})`

3 - x trên 2009 - cho 2 - x trên 2010 - cho 1 - x trên 2011 bằng 1

Cho `ΔABC` có góc `A < 90^o`. Vẽ ra phía ngoài `ΔABC` `2` ` ΔABD ` và `ΔACE` vuông cân tại `A`. `a)` Gọi `M` là trung điểm của `DE`. CM: `AM` vuông góc với `BC`. `b)` Gọi `N` là trung điểm của `BC`. CM: `AN` vuông góc với `DE`.