Bài 2: 

a: Xét ΔABC có

X là trung điểm của BC

Y là trung điểm của AB

Do đó: XY là đường trung bình

=>XY//AC và XY=AC/2=3,5(cm)

hay XZ//AC và XZ=AC

b: Xét tứ giác AZBX có 

Y là trung điểm của AB

Y là trung điểm của ZX

Do đó: AZBX là hình bình hành

mà \(\widehat{AXB}=90^0\)

nên AZBX là hình chữ nhật

d: Xét tứ giác AZXC có

XZ//AC

XZ=AC

Do đó: AZXC là hình bình hành

1 bỏ so

-In order to V(inf): Để làm gì

3 -So as to V(inf): Để làm gì

6 me->her

-Could/can/Will+V(inf)

-Help+O+V/to V

11 ..... me where the nearest post office is?

-Can/could+S+V+wh-questions+S+V?

14 -Shall+S+V(inf)?

17 ........ going to help him revise his lessons

-"be" going to V(inf): Sẽ làm gì( mang tính chắc chắn)

18 -Would+S+love/like+to V/N?

19 -Let's+V(inf)

= Shall+we+V(inf)?

20 -Trong ngữ cảnh này "to V" được dùng với nghĩa "để làm gì"

*Inf: Infinitive

toán đâu mà giải

1. My brother (listen)listened  to music last night. 

2. When I came to see Peter, he (do)was doinghis homework.

3. Mr Manh wishes he (be)were in Paris now.

4. Up to present, Mr John (write)has written more than one hundred novels.

5. Tim (always blame)is always blaming his faults on the others.

6. Mary (write)writes her pen pal once a week.

7. When the milkman came, my family (have)was having dinner.

8. Lan and Maryam (not respond)haven't responded each other for along time.

9. If she (study)studies harder, she (pass)will pass the examination.

10. It's important that you arm (operate)be operated now

1. My brother (listen)listened  to music last night. 

2. When I came to see Peter, he (do)was doinghis homework.

3. Mr Manh wishes he (be)were in Paris now.

4. Up to present, Mr John (write)has written more than one hundred novels.

5. Tim (always blame)is always blaming his faults on the others.

6. Mary (write)writes her pen pal once a week.

7. When the milkman came, my family (have)was having dinner.

8. Lan and Maryam (not respond)haven't responded each other for along time.

9. If she (study)studies harder, she (pass)will pass the examination.

10. It's important that you arm (operate)be operated now

\(PT\Leftrightarrow\left(3x+5\right)\dfrac{x+1}{2}+\left(3x+5\right)\dfrac{2x-2}{3}-\left(3x+5\right)=0\)

\(\Leftrightarrow\left(3x+5\right)\left(\dfrac{x+1}{2}+\dfrac{2x-2}{3}-1\right)=0\)

\(\Leftrightarrow\left(3x+5\right)\dfrac{3\left(x+1\right)+2\left(2x-2\right)-6}{6}=0\)

\(\Leftrightarrow\left(3x+5\right)\dfrac{7x-7}{6}=0\)

\(\Leftrightarrow\left(3x+5\right)\left(x-1\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}x=\dfrac{-5}{3}\\x=1\end{matrix}\right.\)

KL: Phương trình có tập nghiệm \(S=\left\{\dfrac{-5}{3};1\right\}\)

g, cộng 1 vào cả 2 vế của pt , ta được :

<=>\(\dfrac{x+1}{7}+1+\dfrac{x+2}{6}=\dfrac{x+3}{5}+1-\dfrac{x+4}{4}+1=0\)

<=>\(\dfrac{x+8}{7}+\dfrac{x+8}{6}-\dfrac{x+8}{5}+\dfrac{x+8}{4}=0\)

<=>\(\left(x+8\right)\left(\dfrac{1}{7}+\dfrac{1}{6}-\dfrac{1}{5}+\dfrac{1}{4}\right)=0\)

<=> x+8 =0 

<=> x=-8

h, 

\(\dfrac{3x-2}{3}\left(x-1\right)+\dfrac{3x-2}{4}\left(2x-2\right)=0\)

<=>\(\dfrac{3x-2}{3}\left(x-1\right)+2.\dfrac{3x-2}{4}\left(x-1\right)=0\)

<=>\(\dfrac{3x-2}{3}\left(x-1\right)+\dfrac{6x-4}{4}\left(x-1\right)=0\)

<=>\(\left(x-1\right).\left(\dfrac{3x-2}{3}+\dfrac{6x-4}{4}\right)=0\)

<=>x-1 =0 

<=> x=1