涛涛1-6答案是不是错了？

grassgreen

Q6:

If x and y are positive, what is the value of x – y?

(1)     (x² – y²) / (x + y) = 4

(2)     x + y = 7

 

A. Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient.

B. Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient.

C. BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient.

D. EACH statement ALONE is sufficient.

E. Statements (1) and (2) TOGETHER are NOT sufficient.

Answer: A

怎么会是A呢？应该是C啊。(1)与(2)结合才能得到x-y的值才对。

向大家请教

BruceNornia

事实上是不用的，题目我不翻译了

 (x² – y²)  = (x + y) (x - y)

从而 条件(1)中 4 = (x² – y²) / (x + y) = (x + y) (x - y) /(x + y) = x - y

 

即不需要x + y的值 就能求出x - y的值

 

The correct answer is A.

Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient.

chriszhx

x² – y² = （x+y）（x-y）

x+y可以消去了，因为都是positive，不会为0

不需要知道x+y=7

grassgreen

so shame

i'm so careless.

Thanks anyway.