在矩形ABCD中,AB=8,AD=6,动点P从A出发,以每秒一个单位的速度沿着A,B,C,D的顺序运动.到D的时候停止.

1.
(a) t ≤8, P在AB上
S = (1/2)*AP*AD = (1/2)*t*6 = 3t
(b) 8 < t ≤ 14, P在BC上
S = (1/2)*AD*AD上的高= (1/2)*6*8 = 24
(c) 14 < t ≤ 22, P在CD上
DP = 22-t
S = (1/2)*DP*AD = (1/2)(22-t)*6 = 3(22 - t)
2.
S = 3t = 15, t = 5
或S=3(22-t) = 15, t =17
3. 有三种可能：
(a)P在AB上, PA =AD = 6
t = 6
(b) P在BC上, 显然P为BC的中点, BP = 3
t = 8 + 3 = 11
(c) P在CD上, AD = DP = 6
t = 8 +6 + (8-6) = 16