$n_{Fe} = \dfrac{16,8}{56} = 0,3(mol) ; n_{O_2} = \dfrac{4,8}{32} = 0,05(mol)$

$3Fe + 2O_2 \xrightarrow{t^o} Fe_3O_4$

0,075         0,05                           0,025                  (mol)

Sau phản ứng : 

$m_{Fe_3O_4} = 0,025.232 = 5,8(gam)$
$m_{Fe\ dư} = 16,8 -0,075.56 = 12,6(gam)$

\(a,VT=9+4\sqrt{5}=\sqrt{5^2}+2.2\sqrt{5}+2^2=\left(\sqrt{5}+2\right)^2=VP\left(dpcm\right)\)

\(b,\sqrt{9-4\sqrt{5}}-\sqrt{5}=-2\)

\(\Leftrightarrow\sqrt{9-4\sqrt{5}}=\sqrt{5}-2\)

Ta có : \(VT=\sqrt{9-4\sqrt{5}}=\sqrt{\sqrt{5^2}-2.2\sqrt{5}+2^2}=\sqrt{\left(\sqrt{5}-2\right)^2}=\left|\sqrt{5}-2\right|=\sqrt{5}-2=VP\left(dpcm\right)\)

máy tính hay tv đấy 

Máy tính như hacker í

là máy tính

24 - 16(x - 1/2) = 23

=> 16(x - 1/2) = 24 - 23

=> 16(x - 1/2) = 1

=> x - 1/2 = 1/16

=> x = 1/16 + 1/2

=> x = 9/16

\(24-16(x-\frac{1}{2})=23\)

\(16(x-\frac{1}{2})=24-23\)

\(16(x-\frac{1}{2})=1\)

\(x-\frac{1}{2}=\frac{1}{16}\)

\(x=\frac{1}{16}+\frac{1}{2}\)

\(x=\frac{9}{16}\)

Vậy số thực x cần tìm là \(\frac{9}{16}\)

Chúc bạn hok tốt ~

I am sorry, I can’t help you.” Peter said to me.

A.   Peter promised to help me.                          B. Peter refused to help me.                   

C. Peter asked me for help.                               D. I couldn’t help Peter.

To make Peter surprised, we _______ and when he comes, we ________.

A. are going to hide / will jump out and shout             B. will hide / are jumping out and shouting

C. are hiding / are going to jump out and shout          D. are hiding / are jumping out and shouting

B

It’s kind of you to help me wash the dishes after the party.

A. Washing the dishes is kind of you to help me.

B. You are so kind when you help me wash the dishes.

C. To help me wash the dishes after the party you are kind.

D. It’s your kind to help me with the dishes after the party.

B