n_Fe = \(\dfrac{14}{56}\) = 0,25 (mol)

a) Fe + 2HCl   →  FeCl₂ + H₂

b)  Theo phương trình phản ứng, ta có

       n_Fe =  2n_HCl = 2.0,25 = 0,5 (mol)

     => m_HCl = 0,5.36,5= 18,25 (mol)

c)   Theo phương trình phản ứng, ta có:

        n_Fe = n_H2 = 0,25 (mol)

       => V_H2= 0,25.22,4 = 5,6 (lít)

a) x³ + 27 + (x+3)(x-9) = 0

⇔ x³ + 27 + x² - 9x +3x - 27 = 0

⇔ x³ + x² - 6x = 0

⇔ x( x² + x - 6 ) = 0

⇔ \(\left[{}\begin{matrix}x=0\\x^2+x-6=0\end{matrix}\right.\) ⇔ \(\left[{}\begin{matrix}x=0\\\left[{}\begin{matrix}x=2\\x=-3\end{matrix}\right.\end{matrix}\right.\)

b) 3x² - 12x = 0

⇔ x(3x -12) = 0     

⇔\(\left[{}\begin{matrix}x=0\\3x-12=0\end{matrix}\right.\) ⇔ \(\left[{}\begin{matrix}x=0\\x=4\end{matrix}\right.\)

a) 1200 : 24 - ( 17 - x) = 36

 ⇔ 50 - 17 + x = 36

 ⇔ 33 + x = 36

 ⇔ x = 3

b)   9 x ( \(x\) + 5 ) = 729

⇔ 9x + 45 = 729

⇔ 9x = 684

⇔ x = 76

đề bài là gì vậy bạn

\(\left\{{}\begin{matrix}2x+3y=-2\\3x-2y=-3\end{matrix}\right.\) ⇔ \(\left\{{}\begin{matrix}6x+9y=-6\\6x-4y=-6\end{matrix}\right.\)⇔ \(\left\{{}\begin{matrix}14y=0\\2x+3y=-2\end{matrix}\right.\)⇔\(\left\{{}\begin{matrix}y=0\\x=-1\end{matrix}\right.\)

“I have already seen this movie”, he said.
=> He said he had already seen that movie

“I am doing my homework today”, she said.
=> She said she was doing her homework that day

“You can go to the movie with your friends”, her father said to her.
=> Her father told her to go to the movie with her friends

“I bought these books yesterday”, she said.
=> She told she had bought those books the day before

I will be busy next month.”, the teacher told his students.
=> The teacher told his students he would be busy the next month

“I knew Don twenty years ago”, said Peter.
=> Peter said he had known Don twenty years before

“I speak Japanese now”, he said.
=> He said he spoken Japanese then

1. were

2. will go

3. Liked

4. watching

5. won't fail

6. Haven't met

A

7.d    8.c   9.d    10.a    11.c    12.c    13.b    14.c    15.b

69.People speak English all over the world.

=> English is spoken all over the world.

70.They were building a new school here when we came.

=> A new house was being built here when we came.

71.He will send his parents a package.

=> A package will be sent to his parents by him.

72.She has bought two new dresses recently.

=> Two new dresses have been bought recently.

73.You must write these music lessons in ink.

=> These music lessons must be written in ink.

74.We saw our friends outside the church.

=> Our friends were seen the church.

75.The little girl puts the gift on the shelf. 

=> The gift is put by the little girl on the shelf.