(1)
x - (-1) = 3 - x
2x = x
x= 1
(2)
显然P在AB外侧
(a) x >3
x - (-1) + x - 3 = 5
2x - 2 = 5
x = 7/2
(b) x < -1
-1 - x + 3 - x = 5
2-2x = 5
x = -3/2
(3)
t分钟时:
x = -t
A:a = -1 - 5t
B:b = 3 - 20t
有两种可能
(a)P在A,B之间
AP = PB
-t - (-1 - 5t) = 3 - 20t - (-t)
t = 2/23
(b)A,B重合
-1 -5t = 3 - 20t
t = 4/15