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

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

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

Sau phản ứng : 

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

ok man

Người nước ngoài à ??

ừ

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

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

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

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

ab bằng 23 nha 

23 nha 

k mình  đi pl 

xin bạn đó 

\(=\dfrac{1}{7}.7-\dfrac{5}{7}-4.\dfrac{1}{4}=1-\dfrac{5}{7}-1=-\dfrac{5}{7}\)

=\(\dfrac{-5}{7}\)

1.I wish someone (offer)…would offer……… to help me with that work tomorrow

2. It’s a pity you didn’t ask…………… him how to get there.  I wish you (ask)had asked him how to get there.

3. Tom wish he (be) ………had been………there yesterday

4. Susan wishes she (can speak)………could speak…. VietNamese

5.     I wish I (be) ………were……..free now

6.     I can’t come tomorrow. I wish I (come)………could ocme……….. tomorrow

7.     The little boy wishes he (become)would become an acrobat……………… when he grows up

8.     I wish I (be)………were ……….. a famous singer

9.     I wish I (see) …………would see………..this film on television again

10.                        I wish they (know)…………had known…….. the truth yesterday

11.                        She wishes her father (be) ……were…………..here now to help her

12.                        I wish they (visit)……………had visited……. us when they were in town.

13.                        I wish someone (give) ……would give……………..me a job next month.

14.                        If only I (can take) …………could take……….the trip to Hanoi with her next summer.

15.                        I wish they (know)………had known………. the truth yesterday.

16.                        I wish I (see)……would see………. that film on TV again.

17.                        We wish she (be)………were………… our teacher of English.

18.                        My brother wishes he (not waste)……hadn't wasted …….. time when he was young.

19.                        They wish they (come)……had come………….. to class on time yesterday morning.

20.                        I wish I ( spend)…………had spent…… my last summer vacation in the mountains.

21.                        I wish she (come) ………had come……..to see me yesterday.

22.                        If only I ( have)……had……….. more time to do this job.

23.                        He missed an exciting football match on TV last night. He wishes he (watch)…had watched …… it.

24.                        I wish you (not give) ……hadn't given………..them my phone number yesterday.

25.                        We wish we (understand) ………had understood……….all the teacher’s explanation yesterday

\(\frac{2004}{2005}\cdot\frac{2005}{2003}\cdot\frac{2003}{2004}=\frac{2004\cdot2005\cdot2003}{2005\cdot2003\cdot2004}=1\)

\(\frac{2004x2005x2003}{2005x2003x2004}\)

Sau đó thì bạn chỉ cần rút gọn thui

Đáp án là 1 nhé

1.

“You’re off to great places, today is your day. Your mountain is waiting, so get on your way.”

2.

“You always pass failure on the way to success.”

3.

“No one is perfect - that’s why pencils have erasers.”

4.

“Winning doesn’t always mean being first. Winning means you’re doing better than you’ve done before.”

5.

“It always seems impossible until it is done.”

6.

“Keep your face to the sunshine and you cannot see a shadow.”

Chuc bạn học tốt!