Answer: E

In other words, the question is looking for which equation cannot have both an x value and a y value that are negative. Choice (A), for instance, is wrong, since whenever x is negative, y is negative. (B) often has two negatives; if x is less than -10, y is negative.

Think in more general terms. What operations always result in a positive number? Even exponents do the trick. (C) has an even exponent, but is not correct due to the "- 2." For instance, if x = -1, y = -1.

That means we should focus on (E). No matter what the value of x, positive or negative, x^4 must be positive, meaning that y must be positive. If y is always positive, it cannot be true that both variables are negative. (E) is correct.