已知x=12，y=$\sqrt{5}$﹣2，求x﹣y的相反数．

Li Ting,15,from Shanghai, was preparing a talk on some western festivals. She searched online for certain information and made PowerPoint presentations(展示).

Wu Qiong，her classmate, was doing his chemistry homework carefully. But he couldn’t work out the last problem even he tried his best. So he took out his mobile phone, opened a special app(应用软件)，and searched the problem. Answers soon appeared on the screen in several seconds.

Nowadays, many students do homework online with the help of the Internet like Li and Wu. They search information online, use apps or discuss through QQ and We chat.

“It's convenient. You don't have to wait for your teacher to explain it to you face to face. "According to Wu." You can also learn by seeing how others work them out. What's more, it improves students' abilities. And it's especially true for new kinds of homework. I am quite skilled at finding information online and using Microsoft Office.”

However, this trend（趋势） also causes problems. Some lazy students just copy the answers online without thinking. Even some ask their classmates to do homework for them. And their teachers don't know the fact.

Anyhow, knowing how to use the Internet is important. The key is to have good self-control. When you come across(遇到) a difficult problem, think about it by yourself first. Be sure to understand the reasons behind the answers after you have turned to the Internet, or you won’t make progress. If you are not sure about your self-control, ask your parents for help.