Câu 21:

\(n_{H_2SO_4}=0,2.2=0,4\left(mol\right)\)

PTHH: Fe + H₂SO₄ → FeSO₄ + H₂

Mol:      x          x

PTHH: 2Al + 3H₂SO₄ → Al₂(SO₄)₃ + 3H₂

Mol:       y         1,5y

Ta có: \(\left\{{}\begin{matrix}56x+27y=11\\x+1,5y=0,4\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}x=0,1\\y=0,2\end{matrix}\right.\)

\(\%m_{Fe}=\dfrac{0,1.56.100\%}{11}=50,91\%\)

\(\%m_{Al}=100-50,91=49,09\%\)

Trả lời đi ạ

\(\left\{{}\begin{matrix}x_1+x_2=2\\x_1x_2=-1\end{matrix}\right.\)

8: \(=\dfrac{x_1^2+x_2^2}{\left(x_1\cdot x_2\right)^2}=\dfrac{2}{1}=2\)

9: \(=\left(x_1+x_2\right)^3-3x_1x_2\left(x_1+x_2\right)=2^3-3\cdot\left(-1\right)\cdot2=8+6=14\)

16: \(=\sqrt{\left(x_1+x_2\right)^2-4x_1x_2}=\sqrt{2^2-4\cdot\left(-1\right)}=\sqrt{4+4}=2\sqrt{2}\)

-25*72+25*21-49*25

=(-25).(72-21+49)

=(-25).100

=(-2500)

bn nhớ k nha

(21/6+5/26)+(7/9+4/180 còn bằng bao nhiêu thì tự tính 

hơ hơ tốt ghê ha HO TRONG HIEU :<

Task 1. Viết lại câu sang so sánh loại 2

1. The apartment is big. The rent is high.

→ The bigger …the apartment is, the higher the rent is………………………………………………………………

2. We set off soon. We will arrive soon.

→ The sooner……we set off, the sooner we will arrive……………………………………………………………

3. The joke is good. The laughter is loud.

→ The better……the joke is, the louder the laughter is………………………………………………………………

4. She gets fat. She feels tired.

→ The fatter …she gets, the more tired she feels………………………………………………………………….

5. As he gets older, he wants to travel less.

→ The older ……he gets, the less he wants to travel ……………………………………………………………….

Task 2. Viết lại câu sang so sánh loại 2

1. If you read many books, you will have much knowledge

→ The more ……books you read, the more knowledge you will have……………………………………………………………….

2. He speaks too much and people feel bored.

→ The more ……he speaks, the more bored people feel……………………………………………………………….

3. The growth in the economy makes people’s living condition better.

→ The more …… the economy grows, the better people's living condition is……………………………………………………………….

4. He learned a lot of things as he traveled far.

 The farther………he  traveled, the more things he learned……………………………………………………………

Task 3. Điền dạng đúng của các từ trong ngoặc để hoàn thành câu so sánh kép loại 1 hoặc 2

1. The weather gets ______colder and colder____________. (cold)

2. Bob is getting _______fatter and fatter_____________. (fat)

3. Jim’s situation became ____more and more difficult_________. (difficult)

4. ___THe older_______ my grandparents get, _______the happier______ they are. (old – happy)

5. ___the hotter_______ it is, ________the weaker___ Hoa is. (hot – weak)

6. The company expended rapidly. It grew ________bigger and bigger______ all the priod. (big)

7. Life got ____better and better______ for Viet as the company became _____more and more successful_____. (good – successful)

8. _______The more_____ we eat, ______the fatter_______ we get. (many – fat)

9. As Microsoft grew, Bill Gates got ________richer and richer_________. (rich)

10. Her job gets __________harder and harder_______ every year. (hard)

IV. Cirle the best option to complete each sentence:

1. The larger the apartment, the................... the rent.

           A. expensive                                                             B. more expensive            

           C. expensively                                                          D. most expensive

2. The faster we walk,………….. we will get there.

           A. the soonest                                                           B. the soon                         

           C. the more soon                                                       D. the sooner

3. The streets are getting more and …………… these days.

           A. crowded                                                                B. less crowded                 

           C. more crowded                                                      D. most crowded

4. The larger the city, …………… the crime rate.

           A. highest                   B. higher      C. the highest              D. the higher

5. Bill is ………………

           A. lazier and lazier    B. more and more lazy

           C. lazier and more lazy                                            D. more lazy and lazier

6. ………………..the time passes, …………….I feel ! The deadline of my thesis is coming, but I have just finished half of it.

           A. The faster / the nervous                                      B. The more fast / the nervous

           C. The fast / the more nervous                                D. The faster / the more nervous   

7. She sat there quietly, but during all that time she was getting…………….Finally she exploded.

           A. more and more angry                                          D. the most angry

           B. the more angry                                                     C. angrier and angrier       

8._______ you study for these exams, _______ you will do.

           A. The harder / the better                                         B. The more / the much

           C. The hardest / the best                                          D. The more hard / the more good

9. His house is _______ mine.

           A. twice as big as                                                      B. as twice big as

           C. as two times big as                                               D. as big as twice

10. The test becomes……….and…………

A. hard/ hard                         B. difficult/ difficult

C. harder/ harder                              D. difficulty/ difficulty

11. His health is getting……….and…………….

A. good/ good                                   B. better/ better

C. bad/ bad                                        D. well/ well

12. The more paper we save,…………preserved.

A. more is wood pulp                      B. the more wood pulp is

C. wood pulp is                                 D. the much wood pulp is

13. The more polluted air we breathe,…….we get.

            A. the more weaker              B. the more weak

            C. the weaker                        D. weaker more

14. The more we study, the……we are.

            A. more good            B. better                     C. better than D. good

15. The more I tried my best to help her, ……….she became.

            A. less lazy                            B. the lazier               C. the more lazy       D. lazier

16. The weather becomes………………

            A. colder with colder                                               B. colder and colder

            C. colder and more colder                           D. more and more cold

17. The more he slept,…………….irritable he became.

            A. the most                            B. the vey more        C. much more           D. the more

18. ………..he worked, the more he earned.

            A. The more hard                 B. The hard               C. The harder D. The hardest

19. ………I get to know Jim, the more I like him.

            A. For more                           B. More                      C. The more  D. The most

20. The competition makes the price of goods……….

            A. most cheap and cheap                            B. cheaper and cheaper

            C. more cheap and more cheap                  D. cheaper and more cheaper

21. That factory is producing…….pollution.

            A. more and more      B. better and better   C. less and least     D. more and less

22. The ………I read about history, the……..it makes me realize how relevant history is for us today.

            A. more/ better                     B. better/ better         C. more/ more           D. better/ more

23. The less we study, the………..we are.

            A. worse                                B. bad             C. well                        D. good

24. ……….the match was, the more spectators it attracted.

            A. The most interesting                               B. The best interesting

            C. The more interesting                               D. The interesting

25. The more running water you use,……………

            A. your bill will be higher               B. will be higher your bill

            C. the higher your bill will be                     D. the highest your bill will be

26..……………you study for these exams, ………..you will do.

          A. The harder/ the better                             B. The more / the much      

          C. The hardest / the best                              D. The more hard / the more good

27. My neighbour is driving me mad! It seems that………….it is at night , ……………he plays his music!

          A. the less / the more loud                           B. the less / less 

          B. the more late / the more loudlier       D. the later / the louder

28. Thanks to the progress of science and technology, our lives have become………….

          A. more and more good                                B. better and better

          C. the more and more good                          D. gooder and gooder

29.The Sears Tower is…………..building in Chicago.

           A. taller           B. the more tall                  C. the tallest            D. taller and taller

30. Peter is……………John.

A. younger and more intelligent than                    B. more young and intelligent than

C. more intelligent and younger than                    D. the more intelligent and younger than

31.Robert does not have………….Peter does.

        A. money more than                                 B. as many money as

        C. more money as                                     D.as much money as

32. It gets…………..when the winter is coming.

        A. cold and cold                                       B. the coldest and coldest    

        C. colder and colder                                 D. more and more cold

33. French is a…………language to learn than English is.

        A. difficult         B. more difficult          C. most difficult        D. more and more difficult

34.A car is……………….than a motorbike.

        A. cheap             B. cheaper                     C. expensive               D. more expensive

35. Thanks to the great effort of doctors and nurses, her health is  getting…………….

        A. worse             B. better                         C. worse and worse   D. better and better

\(-\dfrac{3}{8}=-0,375\\ \dfrac{21}{70}=0,3\)

\(\dfrac{-3}{8}=-0.375\)

\(\dfrac{21}{70}=0.3\)

-(-21+43+7) - (11-53-17)
= -(22+7) - (-42 -17) 
= (-29) - (-59)
= +( 59-29)
=+30 ( hay bn ghi 30 cx đc nha) 
bài này dễ mà

30

~HT~

giúp mình giải thích câu tục ngữ : thuốc đắng giã tật

\(B=\dfrac{3}{2}-\dfrac{2}{21}-\left\{\dfrac{7}{12}-\left[\dfrac{15}{21}-\left(\dfrac{1}{3}-\dfrac{5}{4}\right)-\left(\dfrac{2}{7}+\dfrac{1}{3}\right)\right]\right\}\)

\(B=\dfrac{3}{2}-\dfrac{2}{21}-\left\{\dfrac{7}{12}-\left[\dfrac{15}{21}-\left(-\dfrac{11}{12}\right)-\dfrac{13}{21}\right]\right\}\)

\(B=\dfrac{3}{2}-\dfrac{2}{21}-\left\{\dfrac{7}{12}-\dfrac{85}{84}\right\}\)

\(B=\dfrac{3}{2}-\dfrac{2}{21}-\left(-\dfrac{3}{7}\right)\)

\(B=\dfrac{11}{6}\)