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    Surfing the Internet for fun will make you a better employee, according to an Australian study.

    The University of Melbourne study shows that people who use the Internet for their own reasons at work are about 9 percent more productive(具有创造性的) than those who do not. Study author Brent Coker said, “Surfing the Internet at times helps increase workers' attention.”

    “People need to relax for a bit to get back their attention,” Coker said on the university's website. “Having a short break, such as a quick surfing of the Internet, helps the mind to rest itself, leading to a higher total Internet attention for a day's work, and as a result, increases productivity (生产效率),” he said.

    According to the study of 300 workers, 70 percent of people who use the Internet at work surf the Internet for their own reasons during office hours. Among the most popular surfing activities are searching for information about products, reading online news, playing online games and watching videos. “Firms spend a lot of money on software to block their workers from watching videos, using social networking sites or shopping online,” said Coker. “That's not always a good idea.”

    However, Coker said the study looked at people who surfed the Internet in moderation(适度), or were on the Internet for less than 20 percent of their total time in the office. “Those who spend too much time surfing the Internet will have a lower productivity than those without.” he said.

先试着用笔算，再用计算器验算．

已知$\sin \alpha =-\frac{3}{5},\alpha \in \left(-\frac{\mathrm{\pi }}{2},0\right)$，则$\cos \left(\alpha +\frac{5}{4}\mathrm{\pi }\right)$=（    ）