pls help

[anjaligeorge1]

62. If 2^(-2x) + 2^(-x)-6=0, x-1/x=?

(A) -2
(B) -1
(C) 0
(D) 1
(E) 2

how do i solve thid

[atlantic]

Hi anjaligeorge,

I just did it by testing the solutions.

Started with C (I know, I know, the rule of the thumb says that we should start testing E) and ended with nothing.

Answer is E.

I took me a litle more than 1 min.

I'll try to do it 'mathematically' but remind that GMAT is about finding the right answer. You wont receive any score for solving it beautiful.

[kishore]

If 2^(-2x) + 2^(-x)-6=0, x-1/x=?

2^(-2x) + 2^(-x)-6=0
2^(-2x) + 2^(-x) = 6

If x = -1

2^(-2 *-1)+ 2^(-(-1)) = 6

Therefore x = -1


x-1/x = -1 - 1/(-1) = -1+1 = 0

[atlantic]

Kishore,

One reason why GMAT is taugh, is becouse under time stress one can do silly mistakes.

Review your last calculation. -1-1/(-1) = 2 and not =0. So answer is E not C.

I also do a lot of things like that.

[kishore]

Hey atlantic,

-1-1/(-1) = 2 ????


Please review it properly...it is 0
Let's derive

1/-1 = -1

= > -1 - 1/(-1) = -1-(1/-1) = -1-(-1) = -1+1 = 0

[atlantic]

Kishore,

If the statement says (x-1)/x = ? then I am right

If the statement says x - 1/x = ? then you are right.

For me it was (x-1)/x and so, (-1-1)/-1=2 answer E

???? trapped by the way the statement is written?

[kishore]

question is as below

62. If 2^(-2x) + 2^(-x)-6=0, x-1/x=?

so, i think..i am right

[atlantic]

Parenthesis are often forgotten when people write question in this forum.

If it is x-1/x i think it should be better to write it with spaces on both sides of the subtraction: x - 1/x.

Guess we are both correct but only one got the right answer due to a minor misunderstanding about the question.