????:1?????????:?????????

2???????vx

3??????????

4?????

5????

?2??15????? ????????????????????,???????????????????15??,????????????6.4?????,????

??????????????????,?????????15????4??????????????48?,?????????-?(??49.92?,?????????????88.28?)?????6.4???,???????????????

??,????????????????,???????????????????,?????,???????

?????????????,??????????????,???? ???:????????????????????