bài IX:

1. no sooner returned from his walk than he got down to writing

2. Hard as he worked, he failed

3. you keep calm, you will pass

4. apologized for going to

5.  the song without any

6. em làm đúng rồi

7. it hard to translate this poem

8. had such a fierce dog that nobody dared to enter

9. Hoa nor her brother answered my

10. my clothes to be ironed by my younger sister

bài VIII:

1. I didn't have enough time to go back home for my umbrella.

2. Your cat needed to be looked after properly.

3. There weren't any gifts for me, were they?

4. If only I had studied harder at school.

5. Would you mind coming and collecting me from the station?

6. The harder you work, the more success you get.

7. Minh was not allowed to go out at night by Mr. Ba.

8. You must have been proud of your son's success.

9. I have moved to the construction company for 3 years.

10. The football players are still training.

doi minh 1 lat nha

\(\dfrac{6}{7}=1-\dfrac{1}{7}\)

\(\dfrac{5}{6}=1-\dfrac{1}{6}\)

\(\dfrac{7}{8}=1-\dfrac{1}{8}\)

\(\dfrac{9}{10}=1-\dfrac{1}{10}\)

\(\dfrac{8}{9}=1-\dfrac{1}{9}\)

Do \(\dfrac{1}{10}< \dfrac{1}{9}< \dfrac{1}{8}< \dfrac{1}{7}< \dfrac{1}{6}\)

\(\Rightarrow1-\dfrac{1}{6}< 1-\dfrac{1}{7}< 1-\dfrac{1}{8}< 1-\dfrac{1}{9}< 1-\dfrac{1}{10}\)

\(\Rightarrow\dfrac{5}{6}< \dfrac{6}{7}< \dfrac{7}{8}< \dfrac{8}{9}< \dfrac{9}{10}\)

6/7=1-1/7

5/6=1-1/6

7/8=1-1/8

9/10=1-1/10

8/9=1-1/9

mà 1/6>1/7>1/8>1/9>1/10

nên 5/6<6/7<7/8<8/9<9/10

A = 1,3 - 3,2 +5,1 - 7 +8,9 -10,8+...+43,1

A =  1,3 - 3,2 + 5,1 - 7 +8,9 - 10,8 +...- 41,2 + 43,1 

A = 43,1 - 41,2 +...+8,9 - 7 + 5,1 - 3,2 + 1,3

A = (43,1 - 41,2) +...+ (8,9 -7) + (5,1 -3,2) + 1,3

Đặt B = (43,1 - 41,2) +...+ (8,9 - 7) + (5,1 -3,2) 

Xét dãy số: 5,1; 8,9; ...; 43,1

Dãy số trên có khoảng cách là: 8,9 - 5,1 = 3,8

Dãy số trên có số số hạng là: (43,1 - 5,1):3,8 + 1= 11

Vậy tổng B có 11 nhóm mà mỗi nhóm có giá trị là:

        43,1 - 41,2 = 1,9

B = 1,9 \(\times\) 11 = 20,9

A = 20,9 + 1,3 = 22,2

Bài 7:

a: \(=2006\cdot\left(430-430\right)+100=100\)

b: \(=54\left(7+9-5-1\right)=54\cdot10=540\)

a : 100

b : 540

a : 100   b : 540

Bài 7:

2R+2H₂O\(\rightarrow\)2ROH+H₂

\(n_{H_2}=\dfrac{2,576}{22,4}=0,115mol\)

\(n_R=n_{ROH}=2n_{H_2}=2.0,115=0,23mol\)

\(M_R=\dfrac{8,97}{0,23}=39\left(Kali:K\right)\)

\(m_{KOH}=0,23.56=12,88g\)

\(m_{dd}=8,97+100-0,115.2=108,74g\)

C%KOH=\(\dfrac{12,88}{108,74}.100\approx11,84\%\)

Bài 8:

R+2H₂O\(\rightarrow\)R(OH)₂+H₂

R(OH)₂+2HCl\(\rightarrow\)RCl₂+2H₂O

\(n_{HCl}=0,1mol\)

\(n_R=n_{R\left(OH\right)_2}=\dfrac{1}{2}n_{HCl}=\dfrac{0,1}{2}=0,05mol\)

\(M_R=\dfrac{6,85}{0,05}=137\left(Bari:Ba\right)\)

\(m_{Ba\left(OH\right)_2}=0,05.171=8,55g\)

Bài 9:

-Gọi R là kí hiệu chung cho 2 kim loại kiềm

2R+2H₂O\(\rightarrow\)2ROH+H₂

ROH+HCl\(\rightarrow\)RCl+H₂O

\(n_{H_2}=\dfrac{0,336}{22,4}=0,015mol\)

\(n_{RCl}=n_{ROH}=2n_{H_2}=2.0,015=0,03mol\)

\(M_{RCl}=\dfrac{2,075}{0,03}\approx69,2\)

\(\rightarrow R+35,5=69,2\rightarrow R=33,7\)

Na=23<R=33,7<K=39

a: A(x)=0

=>2x-1=0

=>x=1/2

b: B(x)=0

=>(4x-3)(x+5)=0

=>x=3/4 hoặc x=-5

c: P(x)=0

=>3-x^2=0

=>x^2=3

=>\(x=\pm\sqrt{3}\)

d: M(x)=0

=>9-4x^2=0

=>4x^2=9

=>x=3/2 hoặc x=-3/2

e: N(a)=0

=>2a^2-3a=0

=>a=0; a=3/2