Bài 1:
a) Ta có:
\(a=\dfrac{v-v_0}{t-t_0}=\dfrac{10-50}{20}=-2\) (m/\(s^2\))
=> PTCĐ: \(x=x_0+v_0t+\dfrac{1}{2}at^2\)
  \(\Leftrightarrow\)   \(x=50t+\dfrac{1}{2}.\left(-2\right).t^2\)
  \(\Leftrightarrow\)   \(x=50t-t^2\)
b) Quảng đường vật đi được:
\(S=v_0+\dfrac{1}{2}at^2\)\(=50.20+\dfrac{1}{2}.\left(-2\right).20^2=600\) (m)

a) \(\Rightarrow\left(x-3\right)\left(x+4\right)=5.12\)

\(\Rightarrow x^2+x-72=0\)

\(\Rightarrow\left(x-8\right)\left(x+9\right)=0\)

\(\Rightarrow\left[{}\begin{matrix}x=8\\x=-9\end{matrix}\right.\)

b) \(\Rightarrow\left(x+3\right)^2=36\)

\(\Rightarrow\left[{}\begin{matrix}x+3=6\\x+3=-6\end{matrix}\right.\)\(\Rightarrow\left[{}\begin{matrix}x=3\\x=-9\end{matrix}\right.\)

c) \(\Rightarrow2x^2=8\Rightarrow x^2=4\)

\(\Rightarrow\left[{}\begin{matrix}x=2\\x=-2\end{matrix}\right.\)

2. There used to have many old buildings 10 years ago

3. I wish a new mall didn't build

4. I have had this wardrobe since my wedding day

5. She hasn't been seen for two years

2. There used to be many old buildings 10 years ago.

3. I wish a new mall weren't built here.

4. I have bought this wardrobe since my wedding day.

5. She hasn't been seen (by me) for two years.

Câu 2.

Nhiệt lượng bếp tỏa ra trong thời gian \(t=3min=180s\) là:

\(Q=UIt=RI^2t=60\cdot2,5^2\cdot180=675000J\)

Câu 3.

\(I_{Đ1}=\dfrac{U_{Đ1}}{R_{Đ1}}=\dfrac{6}{6}=1A\)

\(I_{Đ2}=\dfrac{U_{Đ2}}{R_{Đ2}}=\dfrac{1,5}{8}=\dfrac{3}{16}A\)

\(I_b=I_{Đ1}-I_{Đ2}=1-\dfrac{3}{16}=\dfrac{13}{16}A\)

\(R_b=\dfrac{U_b}{I_b}=\dfrac{1,5}{\dfrac{13}{16}}=\dfrac{24}{13}\Omega\)

a: Xét tứ giác OBAC có 

\(\widehat{OBA}+\widehat{OCA}=180^0\)

Do đó: OBAC là tứ giác nội tiếp

Mary if she could speak some foreign languages
Lan if she was going to visit her aunt the day after
what I was doing
how she was feeling then
what I usually did in my free time
why he why he didn't come there to meet her
why I was so lazy and naughty
like playing soccer, don't you?
goes to school late, doesn't he?
can swim very well, can't you?
is going to the party, isn't she?
was published in Germany in 1550, wasn't it?
are sold all over the world, aren't they?
have been built this year, haven't they?
was given a book, wasn't he?
was bought by Mrs Brown yesterday, wasn't she?
is used every day, isn't it?
be beautiful sights in this village when I lived here

nO2 = 5,6/22,4 = 0,25 (mol)

PTHH: 2KClO3 -> (t°, MnO2) 2KCl + 3O2

nKClO3 = 0,25 : 3 . 2 = 1/6 (mol)

nKClO3 = 1/6 . 122,5 = 245/12 (g)

nMg = 2,4/24 = 0,1 (mol)

PTHH: 2Mg + O2 -> (t°) 2MgO

LTL: 0,1/2 < 0,25 => O2 dư

nMgO = 0,1 (mol)

nMgO = 0,1 . 40 = 4 (g)

nO2 = 5,6 : 22,4 = 0,25(mol) 
pthh : 2KClO3 -t--> 2KCl + 3O2
           1/6     <----------------0,25(mol)
=>mKClO3 = 1/6.114,5=229/12(g)

nMg=2,4:24=0,1(mol)
pthh 2Mg+O2 -t-> 2MgO
               0,1--------->0,1(mol) 
=> mMgO = 0,1.40=4 (g) 

nO2 = 5,6/22,4 = 0,25 (mol)

PTHH: 2KClO3 -> (t°, MnO2) 2KCl + 3O2

nKClO3 = 0,25 : 3 . 2 = 1/6 (mol)

nKClO3 = 1/6 . 122,5 = 245/12 (g)

nMg = 2,4/24 = 0,1 (mol)

PTHH: 2Mg + O2 -> (t°) 2MgO

LTL: 0,1/2 < 0,25 => O2 dư

nMgO = 0,1 (mol)

nMgO = 0,1 . 40 = 4 (g)