GWD3-5

Hema

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.

题目中的公式可简化为5（y-1）=r（y-1） （1）r=+-5

等于5时得不出答案 但是等于-5时y可以等于1啊

答案给出选E

我认为选A

谢谢~~~

myice

这道题的确选E，但你的解法是有问题的
y-1不能除，因为y-1可能为0
正确思路是通过原式变形得到 (5-r)(y-1)=0
由(1)知,r=5或-5，如果r=5，那么y可以取任意值，不充分
由(2)知,r=5，y可以取任意值
(1)+(2)同样推不出结论。

但如果这道题把条件2改为r=-5的话，这道题则选C

 

转robert老师的经典回答