【数学讨论稿1-100】10.25起数学讨论稿（10.27更新至100题）

六得飞起

34题还没改吗。。。明显是两条件联立证明x不等于y了啊

XphoenixX

水手Neptune 发表于 2016-11-1 13:50
34.DS：坐标系内有一个直线l，问l 的x intercept 是不是等于y incercept？
条件1：slope＝1
条件2：y inter ...

A的话，有可能是y=x这条线，过原点，那么不就相等啦

水手Neptune

XphoenixX 发表于 2016-11-1 13:52
A的话，有可能是y=x这条线，过原点，那么不就相等啦

soga，那就应该选C！多谢

xmix099

DS：坐标系内有一个直线l，问l的x intercept 是不是等于y incercept？
条件1：slope＝1
条件2：y intercept＝2
解析：
1→斜率=1，y=kx+b则x intercept=-y intercept→NS
2→y intercept＝2,x intercept未知→NS
1,2→l: y=x+2,x intercept=-2,y intercept=2→No
答案：C

Manhattan的数学书写着，No也是答案，不相等就是唯一的答案，所以一定选C

xmix099

Is the average of n consecutive integers equal to 1? (1) n is even.
(2) If S is the sum of the n consecutive integers, then 0 < S < n.

Solution:
4. (D): Statement (1) states that there is an even number of consecutive integers. This statement tells you nothing about the actual values of the integers, but the average of an even number of consecutive integers will never be an integer. Therefore, the average of the n consecutive integers cannot equal 1. SU F F I C I E N T .

Statement (2) tells you that the sum of the n consecutive integers is positive, but smaller than n. Perhaps the most straightforward way to interpret this statement is to express it in terms of the average of the
n numbers, rather than the sum. Average = Sum + Number, so you can reinterpret the statement by dividing the compound inequality by n:This tells you that the average integer in set S is larger than 0 but less than 1. Therefore, the average number in the set does NOT equal 1. SUFFICIENT. The correct answer is (D).
注意上面这句话
As a footnote, this situation can happen ONLY when there is an even number of integers, and when the “middle numbers” in the set are 0 and 1. For example, the set of consecutive integers {0, 1}has a median number of 0.5. Similarly, the set of consecutive integers {-3, - 2, - 1, 0, 1, 2, 3, 4} has a median number of0.5.

水手Neptune

46.DS：问n 是不是24 的factor？
条件1：n 是16 的factor
条件2：n 是12 的factor（可能有误，但是关键信息点是这些）
求助factor是因数还是因子？（因数包括本身）
假设是因数，16:1,2,4,8,16 不充分
12:1,2,3,4,6,12 充分

XphoenixX

83题也有问题吧？

DS:A，B 俩件事独立， 问俩件事都发生的概率<4%?
条件 1: A 发生的概率为 3.5%

都发生就是P(AB)，由于独立，就是P(A)P(B),p(B)最大等于1，所以一定小于4%啊

cocoyj

旅途漫漫 发表于 2016-10-26 11:14
95题 L=6π r应该等于3吧

我也觉得

XphoenixX

95也明显错了吧，周长为6派，当然r=3，怎么会是根号三

XphoenixX

97题答案不对，边长=√((9-5)^2+12^2)=20？,根号里面是160啊