题目

Let us say there is something you don’t know how to do.In the past if you were determined to learn, you might have called a friend or relative, taken a night class or walked down to the local library for a research term. But now a lot of websites are springing up, providing free practical advice on these subjects and actually anything else you can think of.In one sense, these “how-to” sites represent a part of the growing world of online learning. This tradition found one of its earliest forms in the FAQs – or Frequently Asked Questions files – that began on Usenet, the Inter19．函数f（x）=4$\sqrt{x}$+$\sqrt{x（x-1）}$的定义域为{x|x=0或x≥1}．