(0,4) (4,0) (2,0) (4,2) y = -2 + x y = 4 - x
A B C
A 1 0A0A0 0101A1A1 A0A0 0 A1A1 0101
A BC
Lines cross Lines don’t cross
n 1 =8 n 2 =6
(x1,y1)(x1,y1) (x2,y2)(x2,y2) (x3,y3)(x3,y3) (x4,y4)(x4,y4) (x5,y5)(x5,y5) x2-x1x2-x1 (y 1 +y 2 )/2
A B C D AREAAREA A B
A A B 0312 A 0311 B 0313 A 0310 A
park ParkNULL River2 Village20 Well1113 well village
Map (1) A C (2,3) D (4,5) B (14) E (6,7,8)F G (9,10) H (11,12,13)