已知圆C的方程是
(I)如果圆C与直线y=0没有公共点，求实数m的取值范围；
(II)如果圆C过坐标原点，直线l过点P(0，)(0≤a≤2)，且与圆C交于A,B两点，对于每一个确定的a，当△ABC的面积最大时，记直线l的斜率的平方为u，试用含a的代数式表示u，试求u的最大值.
暂无解析
五(6)班图书角书架中的图书，故事书占1/3，漫画类占1/4，科技类占2/5，其余为文体类，文体类占这些书的几分之几?
已知数列an的前n项和Sn=1+λan，其中λ≠0，(Ⅰ)证明an是等比数列，并求其通项公式;
()是习近平新时代中国特色社会主义思想的核心要义。
Jack is a teacher of English. He is not young，but he is not old. He has a round face and black hair.He is tall. There are fifty students in his class. They all like him.Now it's in the afternoon. Look，some students are working in the classroom. Jack is there，too.He is helping them to study English. He is a good teacher， and he is a good friend of them all.
()1. What does Jack do?
A. He is a worker.
B. He is a teacher.
C. He is a doctor.
D. He's a nurse.
()2. What colour is his hair?
A. It's black.
B. His heir is white.
C. It is brown.
D. He has yellow hair.
()3. How many students are there in his class?
A. There are fifteen students in his class.
B. There's fifty.
C. He has fifty.
D. There're fifty in it.
()4. Jack is a good teacher，isn't he?
A. Yes ，he isn't.
B. No ，he is.
C. Yes，he's.
D. Yes ，he is.
()5. What are the students doing in the classroom?
A. They are walking there.
B. They are doing their lessons.
C. They are helping their teacher.
如图,在y>0的区域存在方向沿y轴负方向的匀强电场,场强大小为E，在y<0的区域存在方向垂直于xOy平面向外的匀强磁场。一个氕核11H和一个氚核21H先后从y轴上y=h点以相同的动能射出,速度方向沿x轴正方向。已知11H进入磁场时,速度方向与x轴正方向的夹角为60°,并从坐标原点O处第一次射出磁场。11H的质量为m,电荷量为q不计重力。求
(1)11H第一次进入磁场的位置到原点O的距离
(2)磁场的磁感应强度大小
(3)21H第一次离开磁场的位置到原点O的距离
