Vận tốc của chất điểm:

\(v\left(t\right)=s'\left(t\right)=3t^2-6t+9=3\left(t-1\right)^2+6\ge6\)

Dấu "=" xảy ra khi \(t-1=0\Rightarrow t=1s\)

47.3=141

55.11=605

77.2-154=0

47 . 3 = 141

55 . 11 = 605

77 . 2 - 154 = 0 

T.i.c.k mình nha.MÌnh rùi đó.

=141

=605

=-76.8

a) 

\(n_{Fe_2O_3}=\dfrac{24}{160}=0,15\left(mol\right)\\ n_{H_2SO_4}=0,2.2,5=0,5\left(mol\right)\\ PTHH:Fe_2O_3+3H_2SO_4\rightarrow Fe_2\left(SO_4\right)_3+3H_2O.\\ Vì:\dfrac{0,15}{1}< \dfrac{0,5}{3}\)

=> H₂SO₄ dư, Fe₂O₃ hết => Tính theo Fe₂O₃

Ta có:

 \(n_{H_2SO_4\left(dư\right)}=0,5-\left(0,15.3\right)=0,05\left(mol\right)\\ \Rightarrow m_{H_2SO_4\left(dư\right)}=0,05.98=4,9\left(g\right)\)

b) \(n_{Fe_2\left(SO_4\right)_3}=n_{Fe_2O_3}=0,15\left(mol\right)\)

=> \(m_{Fe_2\left(SO_4\right)_3}=0,15.400=60\left(g\right)\)

c) \(V_{ddFe_2\left(SO_4\right)_3}=V_{ddH_2SO_4}=200\left(ml\right)=0,2\left(l\right)\)

Vậy: \(C_{MddFe_2\left(SO_4\right)_3}=\dfrac{0,15}{0,2}=0,75\left(M\right)\)

nFe2O3= 24/160 = 0,15 mol

nH2SO4 = 0,2.2,5= 0,5 mol

Fe2O3 + 3H2SO4 -> Fe2(SO4)3 + 3H2O

0,15         0,5

ta có 0,15/1 < 0,5/3

=> H2SO4 dư 

Fe2O3 +3H2SO4 -> Fe2(SO4)3 +3H2O

0,15        0,45               0,15 

 nH2SO4 dư = 0,5-0,45=0,05mol

mH2SO4 dư = 05.98=4,9(g)

b, mFe2(SO4)3 = 0,15.400=60(g)

c, C(Fe2(SO4)3) = n/V = 0,15/ 0,2=0,75M

C(H2SO4) dư = n/V = 0,05/0,2= 0,25 M

Câu 9: B

Câu 10: B

Câu 11: A

Câu 12: D

Câu 13: C

Câu 14: A

Câu 15: C

Tham khảo!
There are many advantages and disadvantages of choosing to live in the country or to live in the city. But the advantages of living in the country definitely outweigh the advantages of living in the city.
In the city, public schools are often packed full of students resulting in larger class sizes and no real teacher student relationship. You would be lucky if your teacher could put a name to your face. Though, bigger schools in the city offer more courses for the student to take and also offer more extracurricular activities. Where in the country, public schools often do not have many students making class sizes significantly smaller resulting in a better teacher student relationship. Your teacher usually knows you by first and last name, and chances are, your teacher had a few of your family members as students. Though these things are advantages, school in rural areas generally do not offer as many courses and also do not have as many extracurricular activities to be involved in, limiting the students to fewer opportunities.
There are a lot of activities to do in the city. There are more movie theaters, concerts, professional sporting events, zoos, shopping malls, restaurants and museums. But the activities you can do in the country are a lot more fun. In the country, activities consist of, four wheeling, boating, horseback riding, camping, having bon fires, taking walks in the woods and having back yard barbeques.
Transportation is very accessible in the city. Public transportation, by way of subways, busses, trams and ferries are easy and cheap ways of getting around. But the streets are also very crowded. Whereas owning your own vehicle is a must if you live in the country. Which, when added to the cost of insurance, gas and the time of commuting, can end up being a very large expense. But, with the roads being less crowded, it is a much more peaceful way to travel.
Some may believe that you have to...

\(x^2+4x+3=x^2+3x+x+3=\left(x^2+3x\right)+\left(x+3\right)=x\left(x+3\right)+\left(x+3\right)=\left(x+3\right)\left(x+1\right)\)

m.n giúp mk câu này vs ạ 

(\(\dfrac{x+2}{x-2}-\dfrac{x-2}{x+2}+\dfrac{16}{4-x^2}\)) : (\(\dfrac{4}{2-x}-\dfrac{8}{2x-x^2}\))