Giúp mình với các bạn ạ mình đang cần sự trợ giúp gấp ạ !!! Cho (O;R) , từ điểm M nằm ngoài (O) vẽ các tiếp tuyến MA,MB đến (O) với A; B là tiếp điểm và cát tuyến MCD không đi qua O. a)Chứng minh rằng: MA2= MC.MD. b)Tia phân giác của CAD cắt CD tại E và cắt (O) tạiF.Chứng minh rằng: OF ⊥CD và MA = ME c)Chứng minh rằng: BE là tia phân giác của CBD d)Đường thẳng OF cắt CD tại K và cắt AB kéo dài tại N.Chứng minh rằng NC, ND là các tiếp tuyến của d-đường tròn (O)

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1. Nam started studying English 5 years ago → Nam has .................................................................................................................................. 2. We started to play soccer an hour ago → We have .................................................................................................................................. 3. She started reading this novel a week ago → She has .................................................................................................................................... 4. He started writing this book last year → He has .................................................................................................................................... 5. My sister began playing badminton in 1986 → My sister has .......................................................................................................................... 6. Hoa began playing piano when she was ten → Hoa has ................................................................................................................................... 7. Mr Hai began to be a doctor when he was 21 → Mr Hai has .............................................................................................................................. 8. Hung stopped playing soccer last year → Hung hasn’t ............................................................................................................................ 9. I stopped smoking 2 years ago → I haven’t .................................................................................................................................. 10. She stopped writing when she moved to England → She hasn’t ............................................................................................................................... 11. My brother stopped working in this factory last month → My brother hasn’t ................................................................................................................... 12. Maria stopped planting flowers 10 years ago → Maria hasn’t ............................................................................................................................ 13. Ba started building this hotel a year ago. → Ba has… ................................................................................................................................ 14. She stopped playing volleyball a year ago → She hasn’t .............................................................................................................................. 15. We began listening to music at 4pm → We have… .............................................................................................................................. 16. I left there last month → I haven’t ................................................................................................................................. 17. When did you live here? → How long ...............................................................................................................................? 18. When did you know her? → How long ...............................................................................................................................? 19. How long have you written this book? → When ....................................................................................................................................? 20. Ba has worked in this factory since he was 18 → Ba started ..............................................................................................................................?