Problem:
If x<0, then which of the following must be positive?
Answer Choices:
A. ∣x∣x​
B. −x2
C. −2x
D. −x−1
E. 3x​ Solution:
Choice (D) may be written as −x1​. If x is negative, choice (D) is positive. To see that the other choices need not be positive, let x=−1​ and then