Ex 5:

1. She has lived in HN for 2 years

2. He has studied English since he was young

3. This is the first time I have eaten this kind of food

4. She is the most beautiful girl I have ever met

5. I have never read the best novel before

Ex 6:

1. We haven't eaten out since mom's birthday

2. How long have you lived here?

3. Have you ever been to Russia?

4. She have not met her kids since Xmas

5. Have they repaired the lamps yet?

\(m_{H_2O}=1,62\left(g\right)\Rightarrow n_{H_2O}=0,09\left(mol\right)\Rightarrow n_H=0,18\left(mol\right);m_H=0,18.1=0,18\left(g\right)\\ n_{CO_2}=\dfrac{2,64}{44}=0,06\left(mol\right)\Rightarrow n_C=n_{CO_2}=0,06\left(mol\right);m_C=0,06.12=0,72\left(g\right)\\ Vây:m_C+m_H=0,72+0,18=0,9< 1,38\\ \Rightarrow X.có.chứa.O\\ m_O=1,38-0,9=0,48\left(g\right);n_O=\dfrac{0,48}{16}=0,03\left(mol\right)\\ Đặt.X:C_aH_bO_c\left(a,b,c:nguyên,dương\right)\\ Ta.có:a:b:c=0,06:0,18:0,03=2:6:1\\ \Rightarrow CTĐG:C_2H_6O\\ M_X=23.2=46\left(\dfrac{g}{mol}\right)=M_{C_2H_6O}\\ \Rightarrow X:C_2H_6O\)

\(\Leftrightarrow\left\{{}\begin{matrix}x+\dfrac{1}{3}y=\dfrac{7}{3}\\x-\dfrac{1}{2}y=-\dfrac{1}{6}\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}\dfrac{5}{6}y=\dfrac{5}{2}\\x+\dfrac{1}{3}y=\dfrac{7}{3}\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}y=3\\x=\dfrac{4}{3}\end{matrix}\right.\)

Lời giải:

Lấy PT(1) trừ PT(2) theo vế:

$\frac{y}{3}+\frac{y}{2}=\frac{7}{3}+\frac{1}{6}$

$\Leftrightarrow \frac{5}{6}y=\frac{5}{2}$
$\Leftrightarrow y=3$

$x=\frac{7}{3}-\frac{y}{3}=\frac{7}{3}-1=\frac{4}{3}$

Giúp em giải với huhu