在平面中有4个点A、B、C、D,每过两点作一条直线,最多可作6条直线,如图1所示.这时,我们就说A、B、C、D四个点构成一个点图,使每条直线上刚好有2个点.这时,我们自然会联想到会不会存在一个点图,使每条直线上刚好有3个点?或者要求放宽一点,使每条直线上至少有3个点呢?显然,这种点图是存在的,如图2所示,A、B、C三点在同一直线上.由A、B、C三点所构成 There are 4 points in the plane A, B, C, D, every two points for a straight line, up to 6 straight lines, as shown in Figure 1. At this time, we say A, B, C, D four A point to form a point map, so that each line has exactly 2 points. At this time, we naturally think of whether there will be a point map, so that each line just has 3 points? Or ask for relaxation, Obviously, this kind of point map exists, as shown in Figure 2, A, B, C three points in the same line by the A, B, C three points