\(a^3+b^3+c^3=3abc\)

\(\Rightarrow a^3+b^3+c^3-3abc=0\)

\(\Rightarrow\left(a+b\right)^3-3ab\left(a+b\right)+c^3-3abc=0\)

\(\Rightarrow\left[\left(a+b\right)^3+c^3\right]-3ab\left(a+b+c\right)=0\)

\(\Rightarrow\left(a+b+c\right)\left[\left(a+b\right)^2-\left(a+b\right)c+c^2\right]-3ab\left(a+b+c\right)=0\)

\(\Rightarrow\left(a+b+c\right)\left[\left(a+b\right)^2-c\left(a+b\right)+c^2-3ab\right]=0\)

\(\Rightarrow\left(a+b+c\right)\left(a^2+2ab+b^2-ac-bc+c^2-3ab\right)=0\)

\(\Rightarrow\left(a+b+c\right)\left(a^2+b^2+c^2-ab-ac-bc\right)=0\)

\(\Rightarrow\left(a+b+c\right)\frac{1}{2}\left(2a^2+2b^2+2c^2-2ab-2ac-2bc\right)=0\)

\(\Rightarrow\left(a+b+c\right)\frac{1}{2}\left(a^2-2ab+b^2\right)\left(b^2-2bc+c^2\right)\left(c^2-2ac+a^2\right)=0\)

\(\Rightarrow\left(a+b+c\right)\frac{1}{2}\left(a-b\right)^2+\left(b-c\right)^2+\left(c-a\right)^2=0.\)

vì \(\left(a-b\right)^2\ge0\)

\(\left(b-c\right)^2\ge0\)

\(\left(c-a\right)^2\ge0\)

\(\Rightarrow\left(a-b\right)^2+\left(b-c\right)^2+\left(c-a\right)^2=0\)

\(\Rightarrow a-b=b-c=c-a\)

\(\Rightarrow a=b=c\left(dpcm\right)\)

cho a,b,c là các số dương thỏa mãn : \(â^3+b^3+c^3=3abc\)

tính giá trị của biểu thức sau:
\(\left(\frac{a}{b}-1\right)+\left(\frac{b}{c}-1\right)+\left(\frac{c}{a}-1\right)\)

Câu hỏi của Nguyễn Quang Tiến - Toán lớp 8 - Học toán với OnlineMath

mik ko tập võ nên ko bt ...xin lỗi

I. Choose the word that has the underlined part pronounced differently from that of the others. (1pt)

1. A. camping B. recycle C. vacuum D. communicate

2. A really B. healthy C. regularly D. identify

3. A. purpose B. bottle C. collect D. second

4. A. sofa B. away C. banana D. occasion

II. Choose the right words to fill in the blanks. (2pts)

1. My brother …….table tennis everyday (A. does B. takes C. makes D. plays)

2. My aunt always gives me doll……special occasions. (A. on B. in C. at D. of)

3. If you have a lot of bottles or stamps, your hobby is……(A. dancing B. painting C. collecting D. reading)

4. He keeps sneezing and coughing. I think he has… (A. a sunburn B. the flu C. a toothache D. a stomachache)

5. You should eat……..junk food if you want to stay healthy. (A. more B. much C. fewer D. less)

6. The Japanese eat much fish, ….. they live for a long time. (A. and B. because C. but D. so)

7. We’ve asked people to…..books and clothes to the children. (A. give B. donate C. cut D. both A and

I. Choose the word whose underlined part is pronounced differently from the other. (1pt)

1. A. character B. chemical C. kitchen D. school

2. A. learned B. loved C. enjoyed D. washed

3. A. books B. measures C. students D. lamps

4. A. pan B. match C. lamp D. save

II. Choose the best answer. (1,5pts)

1. Peter doesn’t talk much in public. He’s rather .....(A. reserved B. kind C. sociable D. humorous)

2. Can I speak .......Hoa, please? - This is Nam. (A. with B. to C. for D. out)

3. Mr. Ba enjoys ...... volleyball in his free time. (A. play B. played C. playing D. to play)

4. Nam is ..... because he always helps people when they need helping. (A. humorous B. sociable C. reserved D. helpful)

5. He ......... an interesting book last night . (A. to read B. read C. reads D. reading)

6. She looks at …… in the mirror. (A. her B. herself C. himself D. myself)

III. Reading: read the passage then do the tasks that follow (2,5pts)

On March 3, 1847 Alexander Graham Bell was born in Edinburgh. He was a Scotman although he later emigrated, first to Canada and then to the USA in 1870. In America, he worked with deaf-mute at Boston University. Soon, Bell started experimenting ways of transmitting speech over long distance. This led to the invention of telephone.

1. When was he born?

2. Was he an American?

3. When did he move to the USA?

4. Where did he work in America?

5. What did he invent?

IV. Supply the correct form of verbs. (2,5pts)

1. The moon (go) ………………….around the earth and the earth (move) ……… around the sun.

2. He spends a lot of time (read) …………………books.

3. You ought (study) …………………harder.

4. She is tall enough (play) …………………volleyball.

V. Make meaningful sentences with given words (2,5pts)

1.They/ old/ enough/ go/to school.

2. He/going / visit/ Ha Noi tomorrow?

3. I / usually/ do / homework/ myself.

4. My sister/slim/and/she/hair/long/black

5. My brother/ used / play/ tennis/ but now /he / doesn’t

……………The end…………

I. Choose the word that has the underlined part pronounced differently from that of the others. (1pt)

1. A. hear B. year C. wear D. clear

2. A. boxes B. watches C. washes D. goes

3. A. arrived B. motioned C. ended D. loved

4. A. jeans B. styles C. labels D. students

II. Choose the best answer to complete the sentences: (2pts)

1. She has studied English ………..(for/ since/ at/ about) 3 years.

2. The school is being ………….(repaints/ repaint/ repainting/ repainted) now.

3. This house …………(is / were/ are /was ) built in 2005

4. How long ……….(have/ has/ were / was) you stayed here?

5. She wishes she ……(was/ is/ were /are) a millionair.

6. They have worked in that factory ……… (since/ at/ about/ for) 1990.

7. I wish I ……….(can/ am/ could/ was) play tennis so well as he can.

8. What do you usually do ……… (at/ on/ in/ for) Sunday?

III. Put the verbs in the correct veb forms (2pts)

1. Your report should (write )………………………….in English.

2. I (see) ………………………………………… him several times on TV

3. My mother gets used to (get)…………….. up early in the morning,

4. They (buy)………………………………… the garden some days ago

5. I (learn) ……………………………………… English since I (be) …………………… 11 years old.

6. Be careful! I (just clean) ……………………………………… the floor.

7. He used (wear)....... the same clothes .

IV. Read the passage and choose the best answers. (2pts)

Clothes can tell a lot (1) ………. a person. Some people like very colorful clothes because they want everyone (2)……… at them and they want to be the center of things. (3)………….. people like to wear nice clothes, but their clothes are not (4)………. or fancy. They do not like people to look at them. Clothes today are very different (5)……….. the clothes of the 1800s. One difference is the way they look. For example, in the 1800s, all women (6)……..dress. The dresses all had long skirts. Sometimes they wear short skirts. Sometimes they wear pants. Another difference between 1800 and today is the (7) ……… In the 1800s, clothes were made only from natural kinds of cloth. They were made from cotton, wool, silk, or linen. But today, there are (8) ……. kinds of man made cloth. A lot of clothes are made from nylon, rayon or polyester.

1. A. about B. at C. with D. on

2. A. look B. to look C. looked D. looking

3. A. Each other B. Another C. Others D. Other

4. A. color B. colorfully C. colorful D. colored

5. A. at B. to C. from D. in

6. A. wear B. worn C. wore D. wearing

7. A. cloth B. clothing C. clothe D. clothes

8. A. many B. much C. any D. a little

V. Rewrite each of the sentences so that the meaning stays the same: (2pts)

1. My father started to give up smoking last year. => My father has…………………………

2. We have learned English for 4 years. => We started……………………………………………………..

3. I can solve this problem quickly. => This problem………………………………………..

4. What a pity! I can’t go with you tomorrow, => I wish………………………………………

Câu hỏi của Phuoc Vo - Toán lớp 6 - Học toán với OnlineMath