Cho hệ phương trình: mx+5y=12 x-3y=-5 Xác định giá trị m để phương trình trên có nghiệm duy nhất

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1. The door bell (ring)________________while Tom (watch)__________________television 2.How fast ___________you_________(drive) when the accident (happen)_______________? 3.Anna and Susan(make)______________dinner when Martin(arrive)______________home. 4. The light (go) ______________ out while we (have) _________________ dinner. But it (come)______________ again after about ten minutes. 5. “What ________ you (do) _______ this time yesterday?” – I (work) ____________ on the computer.” 6. It suddenly (begin)_____________rain while Laura (sit)__________________in the garden. 7.It (be) ___________ cold when we (leave) _____________ the house that day, and a light snow (fall) ______________. 8. When I last (see)_________them, they (try)__________to find a new house near their work. 9. I (walk) _____________ along the street when I suddenly (feel) __________ something hit me in the back. I (not/know)__________________what it was. 10.When we(drive)____________down the hill, a strange object (appear)___________in the sky. 11. You (work)_________________in a hotel when I first (meet)______________you. 12. She (cry)_________________when she (hear)_________________ the news. 13. It (rain)________________when I (walking)___________________on the street. 14. Everyone (go)___________________quiet when the concert (begin)___________________ 15. Lan (swim)__________________in the sea when I (see)_____________________her. 16. When my uncle (come) _______________, we (water)__________________ the plants andflowers in the garden. 17. Thu (talk) _______________to her friend, Hoa, on the phone at 9 o’clock last night. 18. Lan (practice) _________________the piano while her sister (read) _____________comics at 7 o’clock last night. 19. The monkeys (climb) _________________ up the trees when we (visit) _______________ the zoo yesterday morning.