1 Life in the country is not as good as life in the city

2 These room are cleaned every evening

3 Would you mind decorating the christmas tree

4 It's the first time I have talked to the headmaster

V

1 have ever met

2 worked

3 reading

4 are looking - seeing

5 was

VI

1A

2A

3D

4D

5B

IV/

1. is not as good as life in the city

2. are cleaned every evening

3. decorating the Christmas tree?

4. the first time I have (ever) talked to the headmaster

V/

1. have ever met

2. worked

3. reading

4. are looking - seeing

5. was

VI/

1a 2a 3d 4d 5b

\(\dfrac{1}{1.2}+\dfrac{1}{2.3}+...+\dfrac{1}{99.100}\\ =1-\dfrac{1}{2}+\dfrac{1}{2}-\dfrac{1}{3}+...+\dfrac{1}{99}-\dfrac{1}{100}\\ =1-\left(\dfrac{1}{2}-\dfrac{1}{2}\right)-\left(\dfrac{1}{3}-\dfrac{1}{3}\right)-...-\left(\dfrac{1}{99}-\dfrac{1}{99}\right)-\dfrac{1}{100}\\ =1-0-0-...-0-\dfrac{1}{100}\\ =1-\dfrac{1}{100}\\ =\dfrac{99}{100}\)

1/1.2 + 1/2.3 + .... + 1/99.100
= 1 - 1/2 + 1/2 - 1/3 + ... + 1/99 - 1/100
= 1 - ( 1/2 - 1/2 ) - ( 1/3 - 1/3 ) - ..... - ( 1/99 - 1/99 ) - 1/100
= 1 - 0 - 0 - .... - 1/100
= 1 - 1/100
= 99/100

a: =căn 16/5*36/5*49=7*4*9/5=252/5

b: =căn 250*2,5=căn 625=25

c: =căn 3/2*2/3=1

d: =5*căn 2*7*căn 2=70

\(\frac{x^2-10x+25}{x^2-5x}=\frac{\left(x-5\right)^2}{x\left(x-5\right)}=\frac{x-5}{x}\) \(\left(ĐKXĐ:\hept{\begin{cases}x\ne0\\x\ne5\end{cases}}\right)\)

Để \(\frac{x-5}{x}=0\Rightarrow x=5\) (Loại)

Vậy không có giá trị \(x\) nào thoả mãn để \(\frac{x^2-10x+25}{x^2-5x}=0\)

Nhân thêm 2 vào F là mọi việc sẽ ez bởi hằng đẳng thức cơ bản:D

a 

c cắt a tại C

c cắt b tại D   suy ra : c vuông góc với b tại D ( t/ c)

c vuông góc với a tại C 

b

Mờ quá

a) Gọi $n_{Mg} = x(mol) ; n_{Al} = y(mol) \Rightarrow 24x + 27y = 25,5(1)$

$n_{N_2} = \dfrac{5,6}{22,4} = 0,25(mol)$

Bảo toàn electron : $2n_{Mg} + 3n_{Al} = 10n_{N_2} \Rightarrow 2x + 3y = 0,25.10(2)$

Từ (1)(2) suy ra :  x = 0,5 ; y = 0,5

$m_{Mg} = 0,5.24 = 12(gam)$
$m_{Al} = 0,5.27 = 13,5(gam)$

b) $n_{Mg(OH)_2} = x = 0,5(mol) ; n_{Al(OH)_3} = y = 0,5(mol)$

$\Rightarrow m_{Kết\ tủa} = 0,5.58 + 0,5.78 = 68(gam)$

3 B

4 D

5 A

6 C

7 B

8 A

9 C

10 B

12 A

12 A

13 D

14 A

15 A

16 C

17 B

18 C

19 A

20 C

21 B

23 C

23 A

24 B

25 B