设（x2+y2）（x2+y2+2）-15=0，则x2+y2的值为______．

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问题填空题

设（x²+y²）（x²+y²+2）-15=0，则x²+y²的值为______．

答案

设t=x²+y²，则原式可化为t²+2t-15=0，

∴t=x²+y²=3或t=x²+y²=-5，

又∵t≥0，

∴x²+y²=3．

改错题

　短文改错（共10小题；每小题1分，满分１0分）

假定英语课上老师要求同桌之间交换修改作文，请你修改你同旧式写的以下作文。文中共有10处语言错误，每句中最多有两处。错误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：把多余的词作斜线（\）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 Ms Smith,

I am secretary of the City Student Union (CSU). We were organizing an art

exhibition for high school students in city. This will be held on the 9^th of July

in the Exhibition Hall of Beihai. More than 1000 painting will be on show, but

high school students and teachers from all the eight districts will come to the event.

As you are very popularly with us Chinese high school students, we’d like to invite

For you to the exhibition. We would be grateful when you could join them that day.

Looking forward to hear from you soon.

Yours,

Li Ming

问答题

简述学生的本质属性。