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标题: 求教一题：QWD 和这两天实际考题很相似 [打印本页]

作者: stormyyu 时间: 2007-12-20 11:30
标题: 求教一题：QWD 和这两天实际考题很相似

S is a set of points in the plane. How many distinct triangles can be drawn that have three of the points in S as vertices?

(1) The number of distinct points in S is 5.

(2) No three of the points in S are collinear.

作者: cloudymind 时间: 2007-12-20 11:40

Should the answer be (C)?

Any three points, if not collinear and not overlapped, should be able to decide a distinct triangle.

And a triangle requires three verticle points to be non collinear and, obviously, not occupying the same spot.

作者: stormyyu 时间: 2007-12-20 11:45

谢谢，上一题的答案是c,再帮我看看下面这道题

In the decimal representation of x, where 0 < x < 1, is the tenths digit of x nonzero?

(1) 16x is an integer.

(2) 8x is an integer.

作者: cloudymind 时间: 2007-12-20 11:59

Since 8x is an integer and x>0 ---> 8x>=1--->x>=0.125, --> tenths digit of x must be nonzero

16x>=1 --> x>= 0.0625 only

So the answer should be (B)

作者: stormyyu 时间: 2007-12-20 16:47
第一个选项既然肯定不满足条件，按道理也应该对呀？

作者: chonheinrich 时间: 2007-12-20 18:55
(1)可以是0.0625， 0.25， 0.5， 0.75，等等等等，所以不确定

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