vigneshpandi wrote:

I am sorry....the question has all the terms 'n' on the powers....the actual question is:

Each of the following equations has at least one solution EXCEPT

1. –2^n = (–2)^-n

2. 2^-n = (–2)^n

3. 2^n = (–2)^-n

4. (–2)^n = –2^n

5. (–2)^-n = –2^-n

The answer is(1)....

While it is possible to reason out which of these choices must not work, we may not have time or the confidence to do so. However, this problem has variable in its answer choice, and relatively simple math. Therefore, an easy alternative is picking numbers.

Since we're dealing with exponents, we want to keep things as easy as possible. Hence, we'll start with the easiest exponent possible: n = 1. A, B, and C are not solved (x^-n = 1/(x^n), so we're comparing integers to fractions), but choices D and E both end up valid, eliminating them from contention.

In the process of doing this, however, we've uncovered a major clue to our next step: A, B, and C, all compared integers to fractions, and the only integer equal to it's reciprocal is 1, which is equal to 1/1. This, in turn, tells us the we need to pick n = 0. Remember, for all non-zero x, x^0 = 1.

If we plug n = 0 into choices B and C, we end up with 1 = 1 both times. Choice A, however, results in the false 1 = -1. Thus, we conclude that the first choice has no valid solutions, and is therefore the correct answer.

_________________

Eli Meyer

Kaplan Teacher

http://www.kaptest.com/GMAT

Prepare with Kaplan and save $150 on a course!

Kaplan Reviews