please explain why x is not the answer
I did ask this question earlier,but since the form of the question was not clear so I am asking again
Square root
This topic has expert replies
-
- Legendary Member
- Posts: 1035
- Joined: Wed Aug 27, 2008 10:56 pm
- Thanked: 104 times
- Followed by:1 members
i would pick a number. since x<0, say x=-2
(-x*|x|)^1/2= [-(-2)*|-2|]^1/2
=> (2*2)^1/2
=2 (a square root is always +ive or 0. (non-negative)
so the expression translates to -x
(-x*|x|)^1/2= [-(-2)*|-2|]^1/2
=> (2*2)^1/2
=2 (a square root is always +ive or 0. (non-negative)
so the expression translates to -x
- gmat740
- MBA Student
- Posts: 1194
- Joined: Sat Aug 16, 2008 9:42 pm
- Location: Paris, France
- Thanked: 71 times
- Followed by:17 members
- GMAT Score:710
The number inside the square root has to be always positive,however the result that is, the answer obtained by taking square root can be positive or negative=2 (a square root is always +ive or 0. (non-negative)
You need to brush up your skills again scoobydbooby
-
- Legendary Member
- Posts: 1035
- Joined: Wed Aug 27, 2008 10:56 pm
- Thanked: 104 times
- Followed by:1 members
for the gmat the number inside the square root has to be positive as otherwise we would be dealing with complex numbers which are not tested on the gmat.
and √(x^2) is equal to |x|. so √(2^2) is always |2| or +2
gmat740,
that was outright rude. always choose your words with caution, you never know when you have to eat them.![Very Happy :D](./images/smilies/grin.png)
and √(x^2) is equal to |x|. so √(2^2) is always |2| or +2
gmat740,
that was outright rude. always choose your words with caution, you never know when you have to eat them.
![Very Happy :D](./images/smilies/grin.png)
-
- Master | Next Rank: 500 Posts
- Posts: 145
- Joined: Mon Feb 16, 2009 8:41 am
- Thanked: 2 times
- Followed by:2 members
Now, now, here's the exact reason:
For all real numbers x,
sqrt{x^2} = |x| = x , if x > 0
= -x, if x < 0
As x<0, so answer is -x.
For all real numbers x,
sqrt{x^2} = |x| = x , if x > 0
= -x, if x < 0
As x<0, so answer is -x.
Asset
-
- Master | Next Rank: 500 Posts
- Posts: 418
- Joined: Wed Jun 11, 2008 5:29 am
- Thanked: 65 times
gmat740, you shouldn't say things like that about other forum members.
As for this problem, I see that you have made a similar reasoning in this post:
https://www.beatthegmat.com/gmat-prep-1- ... tml#139267
I've given the same explanation as what scoobydooby has given here.
-BM-
As for this problem, I see that you have made a similar reasoning in this post:
https://www.beatthegmat.com/gmat-prep-1- ... tml#139267
I've given the same explanation as what scoobydooby has given here.
-BM-