求曲线y=x2在点（3,9）处的切线l1的方程,并求该切线l1与直线l2:6x-y+9=0之间的距离.
用惰性电极电解下列溶液，电解一段时间后，阴极质量增加，电解液的pH下降的是 A. CuCl2 B. AgNO3
某地一天早晨的气温是－7℃，中午上升了11℃，午夜又下降了9℃，则午夜的气温是（ ）. （A）5℃ （B）－5℃ （C）－3
There are some very good things about open education. This way of teaching allows the students to grow as people, and to develop their own interests in many subjects. Open education allows students to
郑渝(郑州至重庆)铁路是中国高速铁路网规划的重要线路，初步规划有①线、②线两种方案。下图左图为郑渝高速铁路规划示意图，右图表示A山地垂直
My friend Jack was the first person I knew ______an iPhone 5S. A. using B. to use C. used D. having used
It is too bad for someone in such a high _______ in the government to behave badly in public. A. position B. situation C. profession D. condition
现在越来越多的国家认识到，反对恐怖主义是一场长期而艰巨的斗争，国际社会必须反对一切形式的恐怖主义，全球反对恐怖主义斗争需要联合国发挥
