阅读理解
Jack was busy last Sunday. His parents were not at home. He walked to the park in the morning. He read English books and did sports there.Then he visited his friend Tom. Tom is his best friend. He is younger and shorter than Jack.They played puzzles together.After lunch, Jack went back home. In the afternoon, Jack cleaned the room and washed the clothes. After finishing these things, his parents got home.
Jack had a nice dinner with his parents. At 10 o'clock, he went to bed.
的外接圆的圆心为
，半径为
，
，且
，则向量
在向量
方向上的投影为( )