rohit_gmat wrote:Please help with this question.... the way i see it, it needs imaginary numbers (i/j) ... but as per my knwledge, this aint tested on the gmat....
OA will be released soon!!!
THANKSS!!!
1) No imaginary numbers needed: since x is negative, -x becomes positive. Since the absolute value is always non-negative, the result of -x|x| is the product of two positive numbers, and the root is taken correctly.
2) However, the question is indeed confusing. Since the answer choices include x, avoid the confusion by plugging in a negative value of x, such as x=-2. If x=-2, then sqrt ( -(-2)|-2|_ = sqrt (2*2) = sqrt(4) = 2. Thus, if we plug in x=-2 into the answer choices, the right answer should equal -2: Eliminate all other answer choices which do not match this goal. Doing this helps you see that the answer is A -(-2)=2, and not D x=-2, which is the strongest trap answer.
While not necessarily faster than algebra (though it can be), plugging in and eliminating is usually the safer way to solve a question with variables in answer choices. The mistakes you are likely to make dealing with abstract algebraic concepts , you are far less likely to do when using real numbers you can wrap your head around. At the end of the day, we choose A not because we have proven that A is the right answer choices algebraically, but rather because none of the other answer choices match our goal, and we know that one answer choice in 5 must be correct: since we've eliminated four answer choices, the last one must be the correct one, and we needn't worry about why.
