x=2015 thì 2013:(2015-2015)=2013:0, biểu thức không có nghĩa 

\(\left|2x-6\right|=3x+1\)

\(\Leftrightarrow\left[{}\begin{matrix}2x-6=3x+1\\6-2x=3x+1\end{matrix}\right.\)

\(\Leftrightarrow\left[{}\begin{matrix}-x=7\\-5x=-5\end{matrix}\right.\)

\(\Leftrightarrow\left[{}\begin{matrix}x=-7\\x=1\end{matrix}\right.\)

Vậy \(S=\left\{1;-7\right\}\)

23

a. \(\left(2x+1\right)^2-4x\left(x-1\right)=4x^2+4x+1-4x^2+4x=8x+1\)

b. \(\left(x-2\right)\left(x+2\right)-\left(x-1\right)^2=x^2-4-x^2+2x-1=2x-5\)

1. B

2. A

3. B

4. D

5. C

Although I enjoy sports every much, but I don't often watch the sports programme

1. Jane's sister doesn't cook as well as Jane

2. In spite of being poor, Tom studied very well

3. Because of her sickness, Mary couldn't go to school

4. Unless you rest yourself, you really will be ill 

5. John said that he had finished studying his lesson

Hông có gì :>

1. I was helped to do my homework by Mary before she went to work yesterday

2. What is being done by you now?

D