a,6784

b,567

lớp 7a trồng đc số cây là

       1020:[8+9]x9=540[cây]

.......7b........................là

        1020-540=480 [cây]

             Đs:chúc  bn   học tốt nha

Đề sai, nãy giờ cứ nghĩ hoài luôn

45²+40²-15²+80.45

=(45²+80,45+40²)-15²

=(45²+2.40.45+40²)-15²

=(45+40)²-15²

=(45+40-15)(45+40+15)

=70.100

=7000

#H

(B có thể dùng máy tính thử lại, kết quả chính xác là 7000)

45^2+40^2-15^2+80*45

=(45+40-15)^2+80.45

=4900+80.45

=4900+3600

=8500

\(A=4x-x^2+3\)

\(A=-\left(x^2-4x-3\right)=-\left(x^2-4x+4\right)+7\)

\(-\left(x-2\right)^2+7\le7\)

dấu "=" xảy ra khi và chỉ khi \(x=2\)

\(< ==>MAX:A=7\)

câu B ko làm đc thiếu dữ kiện có mỗi \(x-x^2\)

\(a,x^2-20x+101\)

\(\left(x^2-20x+100\right)+1=\left(x-10\right)^2+1\ge1\)

dấu "=" xảy ra khi và chỉ khi \(x=10\)

\(< =>MIN=1\)

\(b,4a^2+4a+2\)

\(\left(4a^2+4a+1\right)+1=\left(2a+1\right)^2+1\ge1\)

dấu "=" xảy ra khi và chỉ khi \(a=\frac{1}{2}\)

\(< =>MIN=1\)

\(c,x^2-4xy+5y^2+10x-22y+28\)

\(\left(x^2-4xy+4y^2\right)+10x-20y+\left(y^2-2y+1\right)+27\)

\(\left(x-2y\right)^2+10\left(x-2y\right)+\left(y-1\right)^2+27\)

\(\left(x-2y\right)^2+10\left(x-2y\right)+25+\left(y-1\right)^2+2\)

\(\left(x-2y+5\right)^2+\left(y-1\right)^2+2\ge2\)

dấu "=" xảy ra khi và chỉ khi

\(\hept{\begin{cases}x-2y+5=0\\y-1=0\end{cases}\hept{\begin{cases}x-2y+5=0\\2y-2=0\end{cases}< =>x+3=0< =>x=-3}}\)

\(\hept{\begin{cases}x=-3\\y=1\end{cases}}\)

\(< =>MIN=2\)

a) Ta có: x² - 20x + 101 = x² - 20x + 100 + 1 = (x - 10)² + 1 

Vì (x - 10)² \(\ge\)0 \(\forall\)x \(\in\)R => (x - 10)² + 1 \(\ge\)1

Dấu "=" xảy ra<=> x - 10 = 0 <=> x = 10

Vậy Min x² - 20x + 101 = 1 <=> x = 10

b) Ta có: 4a² + 4a + 2 = 4a² + 4a + 1 + 1 = (2a + 1)² + 1

Do (2a + 1)² \(\ge\)0 \(\forall\)x \(\in\)R => (2a + 1)² + 1 \(\ge\) 1

Dấu "=" xảy ra<=> 2a + 1 = 0 <=> a = -1/2

Vậy min 4a² + 4a + 2 = 1 <=> a = -1/2

a) (x² - 2x + 2)(x² - 2)(x²  + 2x + 2)(x² + 2) = [(x² + 2)² - 4x²](x⁴ - 4) = (x⁴ + 4x² + 4 - 4x²)(x⁴ - 4) = (x⁴ + 4)(x⁴ - 4) = x⁸ - 16

b) (x + 1)³ + (x - 1)³ + x³ - 3x(x + 1)(x - 1) = x³ + 3x² + 3x + 1 + x³ - 3x² + 3x - 1 + x³ - 3x(x² - 1)

 = 3x³ + 6x - 3x³ - 3x = 3x

c) (a + b + c)² + (a + b - c)² + (2a - b)² = a² + b² + c² + 2ab + 2bc + 2ac + a² + b² + c² + 2ab - 2bc - 2ac + 4a² - 4ab + b²

= 6a²  + 3b² + 2c²

d) 100² - 99² + 98² - 97² + ... + 2² - 1

= (100 - 99)(100 + 99) + (98 - 97)(98 + 97) + (96 - 95)(96+ 95) + ... + (2 - 1)(2 + 1)

= 199 + 195 + 191 + ... + 3

= [(199 - 3) : 4 + 1](199 + 3) : 2

= 50.202 : 2

= 5050

e) 3(2² + 1)(2⁴ + 1) ...(2⁶⁴ + 1) + 1 = (2² - 1)(2² + 1)(2⁴ + 1)...(2⁶⁴ + 1) + 1

= (2⁴ - 1)(2⁴ + 1)...(2⁶⁴ + 1) + 1

....

= (2⁶⁴ - 1)(2⁶⁴ + 1) + 1

= 2¹²⁸ - 1 + 1 = 2¹²⁸

f) (a + b + c)² + (a + b - c)² - 2(a + b)² = a² + b² + c² + 2ab + 2bc + 2ac + a² + b² + c² + 2ab - 2bc - 2ac - 2a² - 2b² - 4ab = 2c²

Choose A, B, C or D to indicate the word whose underlined part is pronounced differently from the others.

1. A. solar                            B. perform                          C. enormous                                               D. boring

2. A. reversed                     B. walked                            C. stopped                                               D. obeyed

Choose A, B, C or D to indicate the word that differs from the other three in the position of primary stress in each of the following questions.

3. A. pumpkin                     B. parade                             C. gather                                               D. traffic

4. A. believe                        B. hotel                                C. prefer                                               D. happen

Choose A, B, C or D to indicate the correct answer to each of the following questions.

5. Sunlight is converted _________ electricity by each solar cells in the panels.

A. in                                  B. with                                  C. into                                          D. to

6. Not many people went to see the film. _________ it received good reviews from cris.

A. However,                   B. Although                         C. Despite                                          D. Because

7. A jet pack doesn’t ______ up a lot of space.

A. have                            B. bring                                C. take                                          D. occur

8. At this time next Tuesday, the children _________ “Tom and Jerry” on TV.

A. will watch                  B. will be watching           C. will not be watching                                          D. watch

9. He thinks elephants are _________ animals.  

A. fascinating                 B. fascinated                       C. fascinates                                           D. fascinate

10. Lan ________ in Ha Noi when I was young, but now she doesn’t.

A. be used to living       B. used to live                     C. didn’t use to live                                          D. get used to living

11. A new hydropower station ______ in the North of the country next year.

A. was built                     B. were built                       C. will be built                                          D. has been built

12. Energy can be ________ from wind, hydro and nuclear power.

A. invested                      B. installed                          C. replaced                                          D. generated

13. “Should I use public transport or a bike to reduce carbon dioxide?” – “____________”

A. Of course. It helps to reduce your carbon footprint, you know.

B. Why not? It will harm the environment.

C. I won’t advise you to do so.

D. How about taking your car?

Choose A, B, C or D to indicate the word(s) CLOSEST in meaning to the underlined word(s) in each of the following questions.

14. Despite his broken leg, he went to school.

A. Although                    B. In spite of                        C. Because of                                          D. Nevertheless

Choose A, B, C or D to indicate the word(s) OPPOSITE in meaning to the underlined word(s) in each of the following questions.

15. My brother is fond of pointing out my mistakes.

A. s                             B. knows                              C. supports                                          D. hates

Read the following passage and choose A, B, C or D to indicate the correct answer to each of the questions.

Over the last five years, more and more students from the school have taken part in ______ (16) projects, such as tree planting and cleaning the school grounds. But, no matter how much we do, there’s always more that can be done to improve the place where we live.

This year students from the Conservation Club plan to work with local people to make a community garden near the school. As Tim, a student, says: "No one (17) ________ to live in an unattractive area. If we work together, we can turn these areas into spaces that we can enjoy (18) ________ time in." This kind of local action is not just about the environment. It also helps people to get to know (19) ________ neighbors and it can help build stronger communities.

If you care about your town, and you are interested in paripating in the project, please contact the school for further information.

16. A. environment                B. environmental             C. environmentally                                                   D. environmentalist

17. A. stay                                B. stays                               C. want                                                   D. wants

18. A. spending                       B. giving                             C. paying                                                   D. doing

19. A. her                                 B. its                                    C. their                                                   D. theirs

Read the following passage and choose A, B, C or D to indicate the correct answer to each of the questions.

Visit the Edinburgh Festival

Every year, thousands of people come to Edinburgh, the capital city of Scotland, to be part of the Edinburgh Festival. For three weeks every August and September the city is filled with actors and artists from all over the world. They come to Edinburgh for the biggest arts festival in Britain. During this time, the streets of the city are alive with music and dance from early in the morning untill late at night. You can even see artists painting pictures on the streets.

Ten of thousands of tourists come to the festival to see new films and plays and to hear music played by famous musicians. This year, you can see over five hundred performances with actors from more than forty countries.

The kets for these performances are quite cheap, and it is usually easier to see your favourite star in Edinburgh than it is in London. So come to Edinburgh next summer!

20. What can you even see artists doing on the streets?

A. Playing the guitar

B. Painting pictures

C. Dancing

D. Singing songs

21. The word “they” refers to ________.

A. actors                     B. artists                        C. people                        D. Both A and B are correct

22. Which of following statement is NOT true?

A. You have to pay a lot of money to buy kets.

B. People can join Edinburgh Festival when they visit Scotland.

C. The festival lasts for 21 days.

D. Tourists can see a lot of forms of art in this festival.

Choose A, B, C or D to indicate the underlined part that needs correction in each of the following questions.

23. Once (A) non-renewable (B) energy sources are used out (C), they are gone(D) forever.

24. This is (A) Mr. and Mrs. Evers’ house and (B) those (C) are theirs (D) children.      

Choose A, B, C or D to find out a sentence that has the same meaning as the given one.

25. They released Avengers: Infinity War in April 2018.

A. Avengers: Infinity War are released in April 2018.

B. Avengers: Infinity War was released in April 2018.

C. Avengers: Infinity War released in April 2018.

D. Avengers: Infinity War is released in April 2018.

26. My mom last visited Ho Chi Minh city 3 years ago.

A. My mom didn’t visit Ho Chi Minh city 3 years ago.

B. My mom hasn’t visited Ho Chi Minh city for 3 years.

C. My mom hasn’t visited Ho Chi Minh city for 3 years ago.

D. My mom didn’t visit Ho Chi Minh for 3 years.

27. They were best friends, but they aren’t anymore.

A. They used to best friends.

B. They use to be best friends.

C. They don’t used to best friends.

D. They used to be best friends.

Choose A, B, C or D to find out a sentence that best combine two sentences into a new one. Do not change the given words in any ways.

28. Kenny performed excellently. He didn’t win an Oscar for Best Actor.

A. Despite performing excellently, he didn’t win an Oscar for Best Actor.

B. Despite of performing excellently, he didn’t win an Oscar for Best Actor.

C. Because he didn’t win an Oscar for Best Actor, he performed excellently.

D. He didn’t win an Oscar for Best Actor in spite he performed excellently.

29. We’ll get there early. We’ll be able to get kets.

A. If we get there early, we won’t be able to get kets.

B. If we don’t get there early, we’ll be able to get kets.

C. If we get there early, we won’t be able to get kets.

D. Unless we get there early, we won’t be able to get kets.

30. Tam is not good at English. I am not good at English.

A. Neither Tam nor I are good at English.

B. Neither Tam nor I am not good at English.

C. Neither Tam nor I am good at English.

D. Neither Tam nor I is good at English.

Sao nhiều thế 

Điều kiện xác định : \(x\ge5\)

ta có : \(\frac{3\sqrt{x-5}}{2}-\frac{2\sqrt{x}-7}{3}=\sqrt{x}-1\Leftrightarrow\frac{3\sqrt{x-5}}{2}=\frac{5\sqrt{x}-10}{3}\)

\(\Leftrightarrow9\sqrt{x-5}=10\left(\sqrt{x}-2\right)\Leftrightarrow81\left(x-5\right)=100\left(x-4\sqrt{x}+4\right)\)

\(\Leftrightarrow19x-400\sqrt{x}+805=0\) tới đây đặt căn x = a rồi giải phương trình bậc hai nhé

bạn xem lại hộ mình , tìm GTLN hay là GTNN nhé

mình tìm GTNN , nếu thấy sai hay có gì cứ nhắn riêng với mình

nếu sai thì mình xin lỗi  nhé

đặt A = x² - 4x 

= (x² - 4x + 4) - 4= (x-2)² - 4

ta có : ( x - 2 )² \(\ge\) 0 \(\forall x\) => (x - 2)² -4 \(\ge\) 0 -4

=> A \(\ge-4\)

dấu " =" xảy ra <=> (x - 2)² =0

                           => x-2 = 0 => x= 2

vậy GTNN của A= -4 tại x = 2 

bạn chỉ cần sửa kết luận là : Vậy GTNN của A là -4 tại x = 2

còn bài làm ok rồi nhé 

Câu 8.

PTK của Ba là 137

PTK của H là 1

PTK của C là 12

PTK của O là 16

Vậy PTK của \(Ba\left(HCO_3\right)_2=137+\left(1+12+16.3\right).2=259đvC\)

Câu 9.

Trong một phân tử \(Ca_3\left(PO_4\right)_2\) có ba nguyên tử Ca và hai nguyên tử P và tám nguyên tử O

Vậy số nguyên tử trong một phân tử \(Ca_3\left(PO_4\right)_2=3+2+8=13\)

Vậy ba phân tử \(Ca_3\left(PO_4\right)_2\) có \(13.3=39\) nguyên tử

Câu 10.

Công thức tổng quát hợp chất là \(R_3\left(PO_4\right)_2\)

\(\%m_{PO_4}=100\%-68,386\%=31,614\%\)

Có \(m_{R_3\left(PO_4\right)_2}=\frac{m_{PO_4}}{\%m_{PO_4}}=\frac{\left(31+16.4\right).2}{31,614\%}\)

\(\rightarrow M_{R_3\left(PO_4\right)_2}=\frac{190}{31,614\%}\approx601\)

\(\rightarrow2M_R+190=601\)

\(\rightarrow M_R=137\)

Vậy R là Bari (KHHH: Ba)