To son, Cecil, Just a quick note before I start in earnest. When I wrote this, you were 8, still a little boy. In 2002, I was called to active duty in the Marine Corps in the war on T
On a Friday night in New York，a poor young man called Jay stood near the subway station，playing this violin．The music was so great that many people slowed down and put some money into his
中，
为
的中点，则异面直线
和
间的距离 ．
，以
为原点，建立如图所示的空间直角坐标系，则
，
，设
公垂线段上的向量为
，则
，即
，
，
，又
，
，所以异面直线