[求助]GWD28-5

ilovecushi

Q5:

Is ½x½< 1?

(1)   ½x + 1½ = 2½x - 1½

(2)    ½x - 3½
            ≠ 0

                  

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:

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答桊是C围什麽不是A呢
从(1)不就知道X围3嘛?

cherylzh

A)

suppose X+1>=0, so X>=-1    (1)

suppose X-1>=0, so X>1      (2)

(1)+(2), so if X>1, x+1=2(x-1), so x=3, ½x½>1

suppose X+1>=0, so X>=-1    (3)

suppose X-1<0, so X<1       (4)

(3)+(4),so if -1<=X<1, x+1=2(1-x), so x=1/3, ½x½<1

B) X<>3

So only if (A)+(B), we will know that ½x½<1, the answer is C

ilovecushi

以下是引用cherylzh在2007-11-12 7:33:00的发言：

A)

suppose X+1>=0, so X>=-1    (1)

suppose X-1>=0, so X>1      (2)

(1)+(2), so if X>1, x+1=2(x-1), so x=3, ½x½>1

suppose X+1>=0, so X>=-1    (3)

suppose X-1<0, so X<1       (4)

(3)+(4),so if -1<=X<1, x+1=2(1-x), so x=1/3, ½x½<1

B) X<>3

So only if (A)+(B), we will know that ½x½<1, the answer is C

对不起 脑袋容量不是很大
容我再稳~~
(3)是哪裡来的
围什麼跟(1)一养?