9 Although the girl works hard from morning till night, her step mother isn't happy

10 Rice is grown in tropical countries

11 The countryside is more peaceful than the city, but I prefer living in the city

12 A lot of Chung Cakes are made on Tet holiday

13 Although Little Pea works hard from morning till night, her mother isn't happy

14 An ordinary car goes more slowly than a sport car

15 An's sister performs better than him

16 Many fesstivals are held by the Thai every year

17 I enjoy hanging out with my best friends

18 If you don't hurry up, you will be late for the race

Áp dụng ĐLBTKL, ta có:

\(m_{O_2}=36,1-23,3=12,8g\)

\(\rightarrow V_{O_2}=\dfrac{12,8}{32}.22,4=8,96l\)

Gọi \(\left\{{}\begin{matrix}n_{Mg}=x\\n_{Zn}=y\end{matrix}\right.\)

\(2Mg+O_2\rightarrow\left(t^o\right)2MgO\)

  x       1/2 x               x          ( mol )

\(2Zn+O_2\rightarrow\left(t^o\right)2ZnO\)

 y        1/2 y              y          ( mol )

Ta có:

\(\left\{{}\begin{matrix}24x+65y=23,3\\\dfrac{1}{2}x+\dfrac{1}{2}y=0,4\end{matrix}\right.\) \(\Leftrightarrow\left\{{}\begin{matrix}x=0,7\\y=0,1\end{matrix}\right.\)

\(\rightarrow\left\{{}\begin{matrix}m_{Mg}=0,7.24=16,8g\\m_{Zn}=0,1.65=6,5g\end{matrix}\right.\)

3)

2Mg+O2-to>2MgO

x-------1\2x----------x

2Zn+O2-to>2ZnO

y-------1\2y------------y

ta có \(\left\{{}\begin{matrix}24x+65y=23,3\\40x+81y=36,1\end{matrix}\right.\)

=>x=0,7  mol, y=0,1 mol

=>VO2=0,4.22,4=8,96l

=>m Mg=24.0,7=16,8g

=>m Zn=65.01,=6,5g

Vì  nên tồn tại α thỏa mãn 

(*) ⇔ cos α.cos 2x + sin α. sin 2x = 1

Vậy phương trình có họ nghiệm 

 (k ∈ Z)

với α thỏa mãn 

ko thấy đề

?

Bài 8:

a: Thay x=16 vào P, ta được:

\(P=\dfrac{4+2}{4-1}=\dfrac{6}{3}=2\)

b: Thay \(x=3+2\sqrt{2}\) vào P, ta được:

\(P=\dfrac{\sqrt{2}+1+2}{\sqrt{2}+1-1}=\dfrac{3+\sqrt{2}}{\sqrt{2}}=3\sqrt{2}+2\)

Part 3

I

1 T

2 F

II

3 My family can receive much happiness from doing volunteer

4 My family raises some fund for them, and also cook meal for them

Part IV

I

1 Although I was tired last night, I stayed up late to watch a game show

2 Ha noi is smaller than HCM City

II

1 Sleep more, but try to wake up at the usual time

2 Be careful with what you eat and drink

III

1 - B

2 - D

3 - A

4 - E

5 - F

B

6 so

7 or

8 because

9 and

10 more

Bài 6:

a) Xét ΔBAC vuông tại A và ΔBAD vuông tại A có 

BA chung

AC=AD(gt)

Do đó: ΔBAC=ΔBAD(hai cạnh góc vuông)

Suy ra: \(\widehat{CBA}=\widehat{DBA}\)(hai góc tương ứng)

hay BA là tia phân giác của \(\widehat{DBC}\)

(-100):(x+5)=-5

x+5=-100:(-5)

x+5=20

x=20-5

x=15

=> -5(x+5)=-100

=>x+5=20

=>x=20-5=15

Vậy x=15

thấy đúng thì k hộ chị nha,chúc e học tốt

                      MÌNH CHỌN ĐÁP ÁN:   C