Quite Confusing

This topic has expert replies
Senior | Next Rank: 100 Posts
Posts: 65
Joined: Thu Jul 02, 2009 10:38 pm
Location: Bangalore
Thanked: 1 times

Quite Confusing

by engg.manik » Thu Oct 08, 2009 3:14 am
Q. If x<0, simplify the given expression in terms of x,

[(x-3)^4]^1/4+(-x*absolute value of x)^1/2=?

Master | Next Rank: 500 Posts
Posts: 182
Joined: Sun Aug 02, 2009 7:19 pm
Thanked: 18 times
GMAT Score:680

by sanjana » Thu Oct 08, 2009 3:56 am
IMO : 2X-3

((x-3)^4)^1/4 = (x-3)

(-x|x|)^1/2

Since x<0 , -x will be same as x
|x| will be = x,even though x is -ve

Hence,(-x|x|)^1/2 = (x^2)^1/2 = x

hence, x-3+x = 2x-3

Senior | Next Rank: 100 Posts
Posts: 65
Joined: Thu Jul 02, 2009 10:38 pm
Location: Bangalore
Thanked: 1 times

by engg.manik » Fri Oct 09, 2009 7:42 am
NO the correct answer is 3-2x

Master | Next Rank: 500 Posts
Posts: 182
Joined: Sun Aug 02, 2009 7:19 pm
Thanked: 18 times
GMAT Score:680

by sanjana » Fri Oct 09, 2009 7:45 am
Can Someone help?
Not sure where I went wrong!

User avatar
Senior | Next Rank: 100 Posts
Posts: 55
Joined: Mon Sep 07, 2009 9:11 pm
Location: California
Thanked: 4 times

by nithi_mystics » Fri Oct 09, 2009 8:01 am
Sanjana,

Your solution is also right but if it is not there as one of our answer options, we'll have to check if there is any other way to solve the equation.

Now,

((x-3)^4)^1/4 = (x-3) or (3-x)

Thats because (x-3)^4 = (3-x)^4

Similarly (-x|x|)^1/2 = x or -x

So, ((x-3)^4)^1/4 + (-x|x|)^1/2 can two solutions.

1) x-3+x = 2x-3
2) 3-x-x = 3-2x

The answer choice should have any one of these.

Hope I am clear.
Thanks
Nithi