| 1 |
| 2 |
| 1 |
| 2 |
| 4 |
| x+y |
乙队完成任务需要的时间为
| 1 |
| x |
| 1 |
| y |
| x+y |
| xy |
所以甲、乙两队完成任务需要的时间分别为
| 4 |
| x+y |
| x+y |
| xy |
（2）t1−t2＝
| 4 |
| x+y |
| x+y |
| xy |
| 4xy−(x+y)2 |
| xy(x+y) |
| −(x−y)2 |
| xy(x+y) |
∵x≠y，x＞0，y＞0，
∴（x-y）2＞0，xy（x+y）＞0
∴-（x-y）2＜0，
∴
| −(x−y)2 |
| xy(x+y) |
即t1-t2＜0，∴t1＜t2
∴甲队先完成任务．
| 1 |
| 2 |
| 1 |
| 2 |
| 4 |
| x+y |
| 1 |
| x |
| 1 |
| y |
| x+y |
| xy |
| 4 |
| x+y |
| x+y |
| xy |
| 4 |
| x+y |
| x+y |
| xy |
| 4xy−(x+y)2 |
| xy(x+y) |
| −(x−y)2 |
| xy(x+y) |
| −(x−y)2 |
| xy(x+y) |