[求助]GWD31 1-5

Q5:

Is x > k?

(1)     2^x • 2^k = 4

(2)     9^x • 3^k = 81

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: C

求解析，我排除了A、B、D。但是就不知道C和E哪个对呢？！

多谢NN

(1)x+k=2

(2)2x+k=4

(1)和(2)单独都无法确定xk的值，也无法确定x和k的大小关系，故单独不成立。

(1)和(2)结合有唯一解x=2，k=0，可知x》k。

故选c

(1)x+k=2

(2)2x+k=4

是假设吗？怎么假设的呢？

谢谢

我很笨

(1)     2^x • 2^k = 4推出2^(x+k)=2^2,所以 x+k=2

(2)     9^x • 3^k = 81推出3^(2x+k)=3^4, 所以2x+k=4

这回明白没

明白啦~感激涕零~