Xét ΔAMB vuông tại M và ΔANC vuông tại N có

AB=AC

\(\hat{MAB}\) chung

Do đó: ΔAMB=ΔANC

=>AM=AN và BM=CN

Xét ΔABC có \(\frac{AM}{AC}=\frac{AN}{AB}\)

nên MN//BC

Xét tứ giác BNMC có MN//BC

nên BNMC là hình thang

Hình thang BNMC có BM=NC

nên BNMC là hình thang cân

Sửa đề: \(P=x^4+2x^2+2\left(x^2+1\right)\left(x^2+6x-1\right)+\left(x^2-6x+1\right)^2\)

\(=x^4+2x^2+1+2\cdot\left(x^2+1\right)\left(x^2+6x-1\right)+\left(x^2-6x+1\right)^2-1\)

\(=\left(x^2+1\right)^2+2\cdot\left(x^2+1\right)\left(x^2+6x-1\right)+\left(x^2+6x-1\right)^2-1\)

\(=\left(x^2+1+x^2+6x-1\right)^2-1=\left(2x^2+6x\right)^2-1\)

\(=99^2-1=\left(99-1\right)\left(99+1\right)=98\cdot100=9800\)

Sửa đề: \(P=x^4+2x^2+2\left(x^2+1\right)\left(x^2+6x-1\right)+\left(x^2-6x+1\right)^2\)

\(=x^4+2x^2+1+2\cdot\left(x^2+1\right)\left(x^2+6x-1\right)+\left(x^2-6x+1\right)^2-1\)

\(=\left(x^2+1\right)^2+2\cdot\left(x^2+1\right)\left(x^2+6x-1\right)+\left(x^2+6x-1\right)^2-1\)

\(=\left(x^2+1+x^2+6x-1\right)^2-1=\left(2x^2+6x\right)^2-1\)

\(=99^2-1=\left(99-1\right)\left(99+1\right)=98\cdot100=9800\)

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

1. A. arrive B. sight C. island D. prison

2. A. base B. final C. ancient D. decorate

II. Choose the word whose main stress is placed differently from the others. (0.5 pt)

1. A. perform B. custom C. century D. popular

2. A. collect B. bamboo C. product D. decide

III . Choose the best answer. (2pts)

1. Many young people are fond .............. playing soccer.

A. in B. of C. at D. on

2. I’ve ........................... finished this novel.

A. already b. for C. since D. yet

3. She asked me .................a big house.

A. if I had B. if I have C. Whether I have D. both B& C

4. They tried to make a fire by .....................pieces of bamboo together.

A. adding B. separating C. rubbing D. collecting

5. Would you mind .......................the air- conditioner?

A. if I turn on B. if I turning on C. if I turned on D. turn on

6. She said, “ I must go now.”

A. She said she had to go now. B. She said she has to go then.

C. She said she has to go now. D. She said she had to go then.

7. They are always ………………..video games.

A. play B. playing C. to play D. played

8. I’m very sorry for behaving ………….. last night.

A. bad

B. badly

C. well

D. good

III. Supply the correct forms of the verbs in the brackets. (0,5pt)

1.Mr Hai used to (work) ......work...................in Ha Noi last year.

2.Would you mind if I (play)................played................... video games in here?.

Ta thấy \(8x^3+27y^3\)

\(=\left(2x\right)^3+\left(3y\right)^3\)

\(=\left(2x+3y\right)\left(4x^2-6xy+9y^2\right)\)

\(=4x^2-6xy+9y^2\)

Thế thì \(A=6x^2-6xy+18y^2+5\)

Rồi lại thay \(x=\dfrac{1-3y}{2}\) vào A thôi.

mai mk phải nộp rồi 

\(x+3y=8\Leftrightarrow x=8-3y\)

 Từ đó \(A=4\left(8-3y\right)^2+y^2\)

\(A=4\left(9y^2-48y+64\right)+y^2\)

\(A=37y^2-192y+256\)

 Đến đây bạn làm tương tự như tìm GTNN của tam thức bậc 2 bình thường nhé.

Mình đang mắc chỗ này, bạn giải tiếp nốt giúp m với

1. My son is crazy about playing computer games

2.Are the students interested in playing games?

3. We are not keen on making models because we are not patient enough

4.We are not interested into cooking because I often cut myself

5.My friends are fond of doing aerobics and they go to the gym every twice a day

6. John likes playing computer games in his free time

7. My brother enjoys playing sports and reading books

8.Juila facies doing DIY when she has free time

9. Everyone adore receiving gifts on their birthday

10. I prefer hanging out with my friends to playing board games

`@` `\text {Ans}`

`\downarrow`

`2,`

`a)`

`-5x^2y^4z^5 (-3xyz^2)`

`= (-5).(-3) . (x^2 . x) . (y^4 . y) . (z^5 . z^2)`

`= 15 x^3 y^5 z^7`

Hệ số: `15`

Phần biến: `x^3 y^5 z^7`

Bậc: `3 + 5 + 7 = 15`

`b)`

`12xy^3z^5 .`\((\dfrac{1}{4}x^3z^3)\)

`=`\((12. \dfrac{1}{4})\)`. (x . x^3) . y^3 . (z^5 . z^3)`

`= 3 x^4 y^3 z^8`

Hệ số: `3`

Phần biến: `x^4y^3z^8`

Bậc: `4+3+8 = 15`

`c)`

\(x^3 . (\dfrac{-5}{4}x^2y)(\dfrac{2}{5}x^3y^4)\)

`=`\(\left(-\dfrac{5}{4}\cdot\dfrac{2}{5}\right)\left(x^3\cdot x^2\cdot x^3\right)\left(y\cdot y^4\right)\)

`=`\(-\dfrac{1}{2}x^8y^5\)

Hệ số: \(-\dfrac{1}{2}\)

Phần biến: `x^8y^5`

Bậc: `8 + 5 = 13`