If def < 0 and ef > 0, which of the following must be positive? Choose the correct answer:
A) xy
B) xz
C) (d^2)ef
D) d(e^2)f
E) xy(z^2)
Given that ef is positive and def is negative, you can say that a MUST be negative. As for e and f either they are both positive or both negative.   Option (C) has d^2 which is positive and ef which is positive. So ((d^2)ef) must be positive.
<result>C</result>
If def < 0 and ef > 0, which of the following must be positive?