\(a,\left\{{}\begin{matrix}Az\perp Ox\\Ox\perp Oy\left(\widehat{xOy}=90^0\right)\end{matrix}\right.\Rightarrow Az//Oy\)

\(b,\widehat{xOm}=\dfrac{1}{2}\widehat{xOy}=\dfrac{1}{2}\cdot90^0=45^0\left(t/c.phân.giác\right)\\ \widehat{nAx}=\dfrac{1}{2}\widehat{xAz}=\dfrac{1}{2}\cdot90^0=45^0\left(t/c.phân.giác\right)\\ \Rightarrow\widehat{xOm}=\widehat{nAx}\left(=45^0\right)\)

Mà 2 góc này ở vị trí đồng vị nên \(Om//An\)

a: Xét ΔABC có 

BD là đường cao

CE là đường cao

BD cắt CE tại H

Do đó: H là trực tâm của ΔABC

hay AM⊥BC

Xét ΔAEC vuông tại E và ΔADB vuông tại D có

góc EAC chung

Do đó: ΔAEC\(\sim\)ΔADB

b: Xét ΔAED và ΔACB có

AE/AC=AD/AB

góc EAD chung

Do đó: ΔAED\(\sim\)ΔACB

\(\left(3x+1\right)^2=9x^2+6x+1\)

\(\left(-4+x\right)^2=16-8x+x^2\)

\(9+12x+4x^2=\left(3+2x\right)^2\)

d giống a, e giống b (đề bị lặp)

a: \(\left(3x+1\right)^2=9x^2+6x+1\)

b: \(\left(-4+x\right)^2=16-8x+x^2\)

c: \(9+12x+4x^2=\left(3+2x\right)^2\)

d: \(\left(3x+1\right)^2=9x^2+6x+1\)

e: \(\left(-4+x\right)^2=16-8x+x^2\)

minh ko chac chan dau nha

30 nha

\(A=\dfrac{3}{2\cdot2}=\dfrac{3}{4}\\ A=\dfrac{3}{2\cdot5}=\dfrac{3}{10}\\ A=\dfrac{3}{2\cdot3}=\dfrac{1}{2}\)

I

1 works - will pass

2 had - would buy

3 come - will phone

4 will feel - don't give

5 closed

6 goes - will be

7 will know - don't reveal

8 have 

9 won

10 will stop

II

1 if I wanted to dance

2 when I had come

3 if John had arrived

4 where Maria parked her car

5 If I had watched the latest film

6 if she could help me

7 they had cleaned the windows

8 he hadn't had time to do his homework

9 her mother would be 50 years old

10 the boss had to sign the letter

Phần trên mình làm ở câu hỏi trước của bạn rồi nhớ.
III.
1. doesn't never drink -> never drinks
2. dressing -> dressed
3. Yes -> No
4. are -> will
5. nine -> ninth
6. Who -> How
7. tooth -> teeth
8. many -> much
9. do -> does
10. at -> in
V.
1. worse
2. as good as
3. wider
4. bigger
5. harder
6. tougher
7. fewer
8. narrower
9. the fastest
10. happier
D.
I.
1. A
2. B
3. D
4. D
5. B
II.
1. It is 3 years since we last went to Spain.
2. We have arrived in Budapest for 2 days.
3. This is the second time I have visited the Stone Forest.
4. Dung is keen on travelling.
5. If you don't turn off all the lights, you will pay more money.

III

1 never => bỏ

2 dressing => dressed

3 Yes => no

4 are you doing => do you do

5 nine => ninth

6 Who => how

7 tooth => teeth

8 many => much

9 do => does

10 at => in

V

1 worse

2 better than

3 wider

4 bigger

5 harder

6 tougher

7 fewer

8 narrower

9 faster

10 happier