TTGWD 4-7

Q7:

If x(x - 5)(x + 2) = 0, is x negative?

(1)     x² – 7x ≠ 0

(2)     x² –2x –15 ≠ 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.

why C?

题干表明x只能是-2、0或5中的一个，问题问的是能否确定为-2，换个角度就是0与5能否肯定被排除。

(1)表明x不等于0或7，不充分。

(2)x^2-2x-15=(x-5)(x+3)不等于0，表明x不等于-3或5，也不充分。

(1)和(2)联系起来就充分了，因为0和5都被排除了。