设z=（x+2y）x2+y2，求。
参考答案：
令u=x+2y，y=x2+y2，根据多元函数的复合函数求导法则得
根据句意填写单词使句子完整。
1. In order to protect the environment, we aren't supposed to throw __ about.
2. I'm standing ______ the window to watch the snow.
3. I don't think that your skirt is __ for the party. It's a barbecue.
4. The panda is the ______ of China.
5. I seldom write a letter to friends but I often __ them on the Internet.
肉种鸡对光照的敏感程度不及蛋种鸡。
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