b, \(Đkxđ:x\le\dfrac{5}{2}\)

Ta có:

\(\sqrt{25-20x+4x^2}+2x=5\)

\(\Leftrightarrow\sqrt{\left(5-2x\right)^2}+2x=5\)

\(\Leftrightarrow\left|5-2x\right|=5-2x\)

\(\Leftrightarrow\left[{}\begin{matrix}5-2x=5-2x\\5-2x=2x-5\end{matrix}\right.\)\(\Leftrightarrow\left[{}\begin{matrix}0x=0\\4x=10\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x\in R\\x=\dfrac{5}{2}\left(tmđk\right)\end{matrix}\right.\)

Vậy \(\left\{x\in R/x\le\dfrac{5}{2}\right\}\)

a,\(Đkxđ:x\ge3\)

Ta có:

\(\sqrt{\left(x-3\right)^2}=3-x\)

\(\Leftrightarrow|x-3|=3-x\)

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

\(TH1:x-3=x-3\Leftrightarrow0x=0\)

\(\Rightarrow\)\(x\in R\) và \(x\ge3\)

\(TH2:x-3=3-x\Leftrightarrow2x=6\Leftrightarrow x=3\)( ko thỏa mãn điều kiện)

vậy \(\left\{x\in R/x\ge3\right\}\)

It is true there have been more students find difficulty staying focused in a class in recent years. Given that distraction in school contributes to the bad performance of students, identifying the reasons behind this trend is key to find the solutions.

There are a number of reasons why students find it hard to pay attention at school. First, digital attraction have been a compelling culprit. As most students having digital devices with Internet access, such as smartphones, they are able to use these devices for activies urelated to learning during the class, such as texting, e-mailing and playing games, which prevents them from listenting to the teacher. Second, background noise level in a class also deteriorate children’s attention. Since the noise may come to the class from the outsides, such as construction sites, which is conducive to the increasing background noise level in classroom, students are not able to listen teacher voice clearly, which acts as an detterent for them to follow teacher’s instructions.

However, there are a great deal of solutions to cope with this problem. First, by banning using smartphones in class, students are not disturbed while they are attending the class. In fact, if they did not have to check their phones continuously, they would be able to catch up with the lesson. In addition, many improvements in class should be applied in order to reduce the level of background noise. By installing sound insulation materials, such as sound reducing-glass, the noise from outside is not able to get to the class, which provides students the quiet environment for learning.

In conclusion, using smartphones and the noise level in class can explain this phenomenon. By prohibit student from using digital devices during class and installing insulation material, students would be more focus in class.

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