GWD-3-05 請問喔

xiao19870205

Q5:

If (y+3)(y-1) – (y-2)(y-1) = r(y-1), what is the value of y?

(1)       r² = 25

(2)       r = 5

                  

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:

我的解題:

題目化簡 : (y+3)(y-1) – (y-2)(y-1) = r(y-1) => (y+3) - (y-2) = r

(1) r² = 25, 所以 r =5 or -5

當 r =5, 則可推出 y= -3 時 會滿足

    r = -5, 無答案

(2)      r = 5 時, 則可推知 y= -3

因此我選 (B).

但答案是給 (E)   我不知道自己哪裡忽略了   

請高手幫忙指導  謝謝~~

applebeer

感觉应该是r不等于5时，才能推出y=1

如果r=5，y任何值都满足情况啊。

因为y不等于1时，有（y+3)-(y-2)=y+3-y+2=5=r

jiroushiren

LZ 的这步：“題目化簡 : (y+3)(y-1) – (y-2)(y-1) = r(y-1) => (y+3) - (y-2) = r  ”   就已经中了GMAC的圈套了 

推成这步   就默认了 Y不等于1       忽略了 Y=1 的情况     当Y+1时   r  为任意值   所以答案为E

 

xiao19870205

感謝  我弄懂了!

謝啦~