如图，Rt△ABC中，∠C=90°，CD=6，以CD为直径的⊙O切AB于G，设AG²=y，AC=x．

（1）求y与x的函数关系式，并指出自变量的取值范围．

（2）利用所求出的函数关系式，求当AC为何值时，才能使得BC与⊙O的直径相等？

（3）△ACB有可能为等腰三角形吗？若可能，请求出x的值；若不可能，请说出理由．

文中共有10处语言错误。每处错误仅涉及一个单词的增加、删除或修改。增加：在缺词处加一个漏字符号（∧），并在其下面写出该加的词。删除：把多余的词用斜线（\）划掉。修改：在错的词下划一横线，并在该词下面写出修改后的词。

注意：1.每处错误及其修改均仅限一词；2.只允许修改10处，多者（从第11处起）不计分。

Dear David,

    Sorry to learn that you've put on weight. Eat too much food in McDonald's and KFC must be the reason, I guess.

    You have to realize that food is not always as healthy as was said in the advertisements. If you know much about them, we will find fried chicken and French fries are rich in fat, sugar and salt. They can make you to gain weight and become sick.

    That you ought to have every day are noodles, rice, fruit and vegetables rather than the junk food. Energy-giving food, body-building food and protective food makes up a balanced diet. In word, you must have an idea of how a healthy diet should be and stick to it.

    I hope my advices can help you improve your health.

Yours,

Li Ming

2×3读作____，表示____个____相加，还表示____个____相加。