中和的原理是什么?
参考答案:
中和处理就是利用中和反应调节废水的酸碱度,使其PH值为6~9。
选词填空
从方框中选择正确的单词并用其适当形式完成下面的句子。
小题1:Are there __________ computers in your classroom?
小题2:You can see two _________ in our school.
小题3:Tony is my friend. I often go to school with .
小题4:Candy, ice cream and cola are ___________ food and drink.
小题5:________ your sister a student?
设A是3阶实对称矩阵,已知A的每行元素之和为3,且有二重特征值λ1=λ2=1.求A的全部特征值、特征向量,并求An.