纸张的偏斜度是指平板纸的长边（短边）与其相对应的长边（短边）的尺寸偏差的最小值。（）
参考答案：错
根据句意或首字母填空，每空一词。
1. My friend likes sports, so she is very a_______.
2. Her father is more s_______ than her mother. He hardly ever laughs.
3. Jane isn't very o_______, she likes to stay at home and do some reading.
4. Mary and Kate are t_______, so they look like the s_______.
5. It is n_______for us to go over our lessons carefully before the exam.
已知二次型
的秩为2． (Ⅰ)求a的值； (Ⅱ)求正交变换x=Qy把f(x1，x2，x3)化为标准形； (Ⅲ)求方程f(x1，x2，x3)=0的解．
的秩为2．