[求助] Prep 数学中的两题

rearn

113.
    11760-!-item-!-187;#058&007855

For a certain set of n numbers, where n > 1, is the average (arithmetic mean) equal to the median?

(1) If the n numbers in the set are listed in increasing order, then the difference between any pair of successive numbers in the set is 2.

(2) The range of the n numbers in the set is 2(n - 1).

请问 B 为什么不行呢？

答案是A

谢谢！：）

28.   3377-!-item-!-187;#058&003297

If xy = 1, what is the value of 2^[(x+y)^2] /  2^[(x-y)^2] ?

 

(A)  2

(B)  4

(C)  8

(D)  16

(E)  32

怎能够算出是16呢？

28.   3377-!-item-!-187;#058&003297

If xy = 1, what is the value of 2^[(x+y)^2] /  2^[(x-y)^2] ?

 

(A)  2

(B)  4

(C)  8

(D)  16

(E)  32

怎能够算出是16呢？

[此贴子已经被作者于2008-8-22 1:36:34编辑过]

xixi1120

1.知道了RANGE是多少没用啊,,它的平均数和中数还是不能确定..举个例子..1,1,1,5,7  和1,1,2,4,7 类似的..总之中间是可以变化的..

2.就是用平方差公式..算出指数是4XY..