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\(m_{NaCl}=\dfrac{150.10}{100}=15\left(g\right)\\ m_{H_2O}=150-15=135\left(g\right)\)
Đong 15 gam NaCl khan, 135 gam nước cho sẵn vào cốc nước. Sau đó hóa tan 15 gam NaCl vào nước, dùng đũa thủy tinh khuấy đều thu được dd như theo yêu cầu của đề bài
ex 4.
1 seeing
2 to pay
3 sneezing
4 to clean up
5 to work
6 cutting
7 to iron - ironing
8 driving
9 to have
10 to invite
11 being
12 to find
13 holding - drinking
14 to repair
15 explaining
ex 5.
2. Pamela continued dancing for an hour.
3. I'd rather sit in the front row.
4. Richard expects to do well.
5. What do you intend to do for the summer?
6. I hate clearing up my room.
7. Helen agreed to go to the party with me.
8. My boss refused to let me leave early.
9. I really look forward to hearing from you soon.
10. What do you want to do this evening?
11. The manager promised to speak to you about this.
12. Fiona succeeded in persuading her father to change his mind.
13. Where do you feel like going this evening?
14. The detective happened to discover the secret.
15. It was very late, but she went on tidying up the kitchen.
ex6.
1. The room will be cleaned today.
2. The car might be stolen.
3. That tree had to be cut down.
4. The old houses are going to be demolished.
5. The picture can't be restored.
6. An appointment must be made in advance.
7. I don't want to be made a fool.
8. The garden has to be looked after.
9. He wants to be served.
10. He is going to be interviewed next week.
Bài 2:
a: \(201^3=8120601\)
b: \(199^3=7880599\)
c: \(52^3-8=140600\)
d: \(23^3-27=12140\)
e: \(99^3=970299\)
f: \(62\cdot58=3596\)
Bài 1:
a: \(\left(2x+y\right)^2-\left(y-2x\right)^2\)
\(=4x^2+4xy+y^2-y^2+4xy-4x^2\)
=8xy
b: \(\left(5x+5\right)^2+10\cdot\left(x-3\right)\left(x+1\right)+x^2-6x+9\)
\(=\left(5x+5\right)^2+2\cdot\left(5x+5\right)\cdot\left(x-3\right)+\left(x-3\right)^2\)
\(=\left(6x+2\right)^2\)
\(=36x^2+24x+4\)
c: \(\left(x-y\right)^3+3xy\left(x-y\right)\)
\(=x^3-3x^2y+3xy^2-y^3+3x^2y-3xy^2\)
\(=x^3-y^3\)
d: \(\left(1-2x\right)\left(1+2x+4x^2\right)+8\left(x-1\right)\left(x^2+x+1\right)\)
\(=1-8x^3+8\left(x^3-1\right)\)
\(=1-8x^3+8x^3-8\)
=-7
a) \(x-3=0\)
\(\Leftrightarrow\) \(x=0+3\)
\(\Leftrightarrow\) \(x=3\)
b) \(2x+6=0\)
\(\Leftrightarrow\) \(2x=0-6\)
\(\Leftrightarrow2x=-6\)
\(\Leftrightarrow x=-3\)
c) \(2x+3=x+9\)
\(\Leftrightarrow2x+3-x=9\)
\(\Leftrightarrow x+3=9\)
\(\Leftrightarrow x=9-3\)
\(\Leftrightarrow x=6\)
d) \(\left(x-4\right)\left(2x+4\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x-4=0\\2x+4=0\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}x=4\\2x+4+\left(-4\right)=0\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}x=4\\x=-2\end{matrix}\right.\)
Câu 14:
Ta có: \(\left\{{}\begin{matrix}\%C=\dfrac{12\cdot2}{28}\approx85,71\%\\\%H=14,29\%\end{matrix}\right.\)
Câu 15: Gọi công thức cần tím là CxHy
Theo bài ra, ta có: \(M_{C_xH_y}=8\cdot2=16\)
Số phân tử Cacbon trong A là \(\dfrac{16\cdot75\%}{12}=1\) (phân tử)
\(\Rightarrow\) Số phân tử Hidro trong A là 4
Vậy CTHH cần tìm là CH4
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