a

c

giá trị lớn nhất của A là 4 ,  sảy ra khi ( n+3)²=0
                                                              n+3=0
                                                               n=-3

(2+4+6+.......+100) (36 x 333 -108 X 111 )
=2x(1+2+3+......+50)[36x111(1x3-3x1)
=2x(1+2+3+......+50)(36x111x0)
=2x(1+2+3+......+50)x0
=0

có,vì nước ta nằm ở nơi giao nhau giữa các luôfng di cư sinh vật, khí hậu mang tính chất nhiệt đới ẩm gió mùa điều kiện thuận lợi cho các loại động vật sinh sông

1.If I had had enough money. I would have taken a taxi.                                     

2.    If I had been interested in the film. I would have gone to the cinema.

3.    If we had taken the wrong turning, We wouldn't have arrived late.                  

4.     If she took exercise regularly, she wouldn't be fat.                             

5.     If you follow the instruction ,you won't ruin everything.                             

6.     If you try harder, you won't fail in the next exam.                              

7.     If we had had your address , we would sent you a Christmas card.

8.     We could have lunch in the garden if it didn't rain.

9.    If I didn't forget my credit card, I couldn’t pay for my groceries.

10.  Alex would have pay the electric bill if the electric company hadn't cut off his power.

11.  If the weather hadn't been bad, the outdoor concert wouldn't have cancelled.

12.  If my brother hadn't been sick yesterday, he would have gone to class.

tứ giác AEDF có góc A =góc E = góc F =90 độ
=>  AEDF là hình chữ nhật
=>EF=AD

a

ta có AD=ED
        BD=CD
=> ABCE là hình thoi

1, Letters are typed in the office by Mary
2,You will be helped by his father tomorrow
3,Human life has been completely changed by science and technology
4,this bottle was broken by Peter
5,English is learnt in the room
6, my mind can be changed by nothing