a: Xét ΔBAC có 

D là trung điểm của AB

M là trung điểm của AC

Do đó: DM là đường trung bình của ΔABC

Suy ra: DM//BC và \(DM=\dfrac{BC}{2}=3.5\left(cm\right)\)

1 Yes, they do

2 Yes, it is

3 They often buy fruits and flowers from the market and decorate their houses

4 They often visit their family and friends

a) \(\Rightarrow\left(n+2\right)+3⋮\left(n+2\right)\)

\(\Rightarrow\left(n+2\right)\inƯ\left(3\right)=\left\{-3;-1;1;3\right\}\)

\(\Rightarrow n\in\left\{-5;-3;-1;1\right\}\)

b) \(\Rightarrow\left(n+1\right)+6⋮\left(n+1\right)\)

\(\Rightarrow\left(n+1\right)\inƯ\left(6\right)=\left\{-6;-3;-2;-1;1;2;3;6\right\}\)

\(\Rightarrow n\in\left\{-7;-4;-3;-2;0;1;2;5\right\}\)

c) \(\Rightarrow\left(n+1\right)^2-\left(n+1\right)+13⋮\left(n+1\right)\)

\(\Rightarrow\left(n+1\right)\inƯ\left(13\right)=\left\{-13;-1;1;13\right\}\)

\(\Rightarrow n\in\left\{-14;-2;0;12\right\}\)

d) \(\Rightarrow\left(n+2\right)^2-\left(n+2\right)+7⋮\left(n+2\right)\)

\(\Rightarrow\left(n+2\right)\inƯ\left(7\right)=\left\{-7;-1;1;7\right\}\)

\(\Rightarrow n\in\left\{-9;-3;-1;5\right\}\)

Bài 4: 

a: \(A=\left(x-5\right)\left(2x+3\right)-2x\left(x-3\right)+x+7\)

\(=2x^2+3x-10x-15-2x^2+6x+x+7\)

=-8

1, That
2, This
3, that
4, those
5, these - that
6, these
7, this
8, that
9, that
10, this
11, those
12, this
13, it
14, these
15, them

16, those

this/that dùng cho ng, vật số ít

this: dùng cho ng, vật ở gần

that: dùng cho ng, vật ở xa

these/those dùng cho ng, vật số nhiều

these: ở gần

those: ở xa

1. this

2. This

3. that

4. those

5. these/ that

6. these

7. This

8. that

9. that

10. this

11. those

12. this

13. it

14. these

15. them

16. those