一道有问题的输血，求讨论

xianmengyao

269.    已知下面4点在一条直线上，问那一点不是在这条直线上？ （其实很简单，但是我昨天睡太少，看了老半天没看懂）
A: 根号2， 2根号15
B: 根号4， 2根号7 （这个不太确定）
C: 根号5，一个很奇怪的根号
D: 仔细看就发现是A的两倍
E: B 的两倍
所以选C

狗主人答案：C
Cyy讨论：题目不全，待补充，不过这道题来说，成倍数的话一定在同一条直线上的。

templars

LS is on the right track.

Let's say in the above question there are four points: (a, b), (c, d); (2a, 2b), (2c, 2d). The first two points form a line with a slope of k. The last two points form a line with the same slope of K. Are these four points on the same line? They have to. Because if they are not, two points will be off the line formed by the other three (since these two lines are parallel). This is contrary to the decription of the stimulus, which says ONLY one point is off the line formed by 4 points.

tingting520

Agree. Check their slop. Say pick point A, check the slop

corresponding to other points. If they are on the same line, slop

should be the same. If we found any point has different slop, then

this point is not on the same line. If we found all slop are

different for other points, then, A is not on the same line.

Any comment?

templars

Well, if only one point is off, as suggested in the stimulus, then the other 4 are on the line. If there are two pairs of coordinates, each pair forms a line, and two lines are parallel, then these 4 coordinates are on the same line! If not, there will be at least 2 points off the line.

zhongyaya

话说成倍数的 不一定在一条直线上吧！比如：（3，1）（5, 3）（6,2）（10,6）就不在一条直线上啊