-
sushanta57021
- Junior | Next Rank: 30 Posts
- Posts: 22
- Joined: Mon Aug 11, 2008 10:35 am
- Thanked: 1 times
Let X = -2
[-(-2){-2}]^1/2
2*2^1/2
4^1/2
2
Note: {}=Absolute value
So x = -x
algebra
This topic has expert replies
Source: Beat The GMAT — Problem Solving |
-
sushanta57021
- Junior | Next Rank: 30 Posts
- Posts: 22
- Joined: Mon Aug 11, 2008 10:35 am
- Thanked: 1 times
Let X = -2
[-(-2){-2}]^1/2
2*2^1/2
4^1/2
2
Note: {}=Absolute value
So x = -x
But 4^1/2 can be +2 or -2.
hence answer can be +X or -X.
please explain.......
[-(-2){-2}]^1/2
2*2^1/2
4^1/2
2
Note: {}=Absolute value
So x = -x
But 4^1/2 can be +2 or -2.
hence answer can be +X or -X.
please explain.......
-
amitabhprasad
- Master | Next Rank: 500 Posts
- Posts: 259
- Joined: Thu Jan 18, 2007 8:30 pm
- Thanked: 16 times
-
dmateer25
- Community Manager
- Posts: 1049
- Joined: Sun Apr 06, 2008 5:15 pm
- Location: Pittsburgh, PA
- Thanked: 113 times
- Followed by:27 members
- GMAT Score:710
4^1/2 is the same as Sqr Rt of 4sushanta57021 wrote:Let X = -2
[-(-2){-2}]^1/2
2*2^1/2
4^1/2
2
Note: {}=Absolute value
So x = -x
But 4^1/2 can be +2 or -2.
hence answer can be +X or -X.
please explain.......
-
sushanta57021
- Junior | Next Rank: 30 Posts
- Posts: 22
- Joined: Mon Aug 11, 2008 10:35 am
- Thanked: 1 times
sorry for posting it twice, but first i posted it in the wrong forum, i.e DS forum.
But anyway, I am not convinced with the answer yet.
We cann't take -X as answer only because X<0.
let me explain:
Say, P = [-X{abs(X)}]^1/2
is there any reason why P has to be positive? P can be negetive also, that means p can be X.
Can some one please clarify?
But anyway, I am not convinced with the answer yet.
We cann't take -X as answer only because X<0.
let me explain:
Say, P = [-X{abs(X)}]^1/2
is there any reason why P has to be positive? P can be negetive also, that means p can be X.
Can some one please clarify?
-
sushanta57021
- Junior | Next Rank: 30 Posts
- Posts: 22
- Joined: Mon Aug 11, 2008 10:35 am
- Thanked: 1 times
well, atleast can some one please tell me whether my logic is right.
I am expecting some answer from you guys.
Thnaks,
Sushanta.
I am expecting some answer from you guys.
Thnaks,
Sushanta.
-
iamcste
- Legendary Member
- Posts: 940
- Joined: Tue Aug 26, 2008 3:22 am
- Thanked: 55 times
- Followed by:1 members
sushanta57021 wrote:sorry for posting it twice, but first i posted it in the wrong forum, i.e DS forum.
But anyway, I am not convinced with the answer yet.
We cann't take -X as answer only because X<0.
let me explain:
Say, P = [-X{abs(X)}]^1/2
is there any reason why P has to be positive? P can be negetive also, that means p can be X.
Can some one please clarify?
Momentarily forget P is positive or negative
we know that x is negative, hence abs(X)=-X
Say, P = [-X{abs(X)}]^1/2
= [-X{-X}]^1/2
= (X^2)^1/2
= square root of ( square of X)
=+ X or -X
But, we know that X is negative no
hence P=-X
( If this is understood, forget what P has to be before calculating and confusion arised from here
when you posted the question in DS, you forgot to mention X <0
Check here
https://www.beatthegmat.com/algebra-t22735.html
hence Logitech said that since outer bracket in solving P is a square root
square root of only positive no is defined
this means he concluded abs(X) was negative
this in turn meant X was negative
This he did since you didnot mention X is negative
Had he known that he would not have done reverse calcns
-
sushanta57021
- Junior | Next Rank: 30 Posts
- Posts: 22
- Joined: Mon Aug 11, 2008 10:35 am
- Thanked: 1 times
P = [-X{abs(X)}]^1/2iamcste wrote:sushanta57021 wrote:sorry for posting it twice, but first i posted it in the wrong forum, i.e DS forum.
But anyway, I am not convinced with the answer yet.
We cann't take -X as answer only because X<0.
let me explain:
Say, P = [-X{abs(X)}]^1/2
is there any reason why P has to be positive? P can be negetive also, that means p can be X.
Can some one please clarify?
Momentarily forget P is positive or negative
we know that x is negative, hence abs(X)=-X
Say, P = [-X{abs(X)}]^1/2
= [-X{-X}]^1/2
= (X^2)^1/2
= square root of ( square of X)
=+ X or -X
But, we know that X is negative no
hence P=-X
( If this is understood, forget what P has to be before calculating and confusion arised from here
when you posted the question in DS, you forgot to mention X <0
Check here
https://www.beatthegmat.com/algebra-t22735.html
hence Logitech said that since outer bracket in solving P is a square root
square root of only positive no is defined
this means he concluded abs(X) was negative
this in turn meant X was negative
This he did since you didnot mention X is negative
Had he known that he would not have done reverse calcns
Say, X= -2, and can we not write:
(-2) = [-(-2){2}]^1/2
if this equation is true, then P can be X.
Sorry for raising the same question over and over, but believe me I am not convinced yet.
P has to be positive or (-X) as X<0
how come this true
-
jimmiejaz
- Master | Next Rank: 500 Posts
- Posts: 207
- Joined: Sun Mar 11, 2007 6:16 pm
- Location: Mumbai
- Thanked: 11 times
Well, i understand your confusion.sushanta57021 wrote:sorry for posting it twice, but first i posted it in the wrong forum, i.e DS forum.
But anyway, I am not convinced with the answer yet.
We cann't take -X as answer only because X<0.
let me explain:
Say, P = [-X{abs(X)}]^1/2
is there any reason why P has to be positive? P can be negetive also, that means p can be X.
Can some one please clarify?
But, sqrt(-ve number) gives us a complex number.
Here we are given that x<0.
Lets go according to you,
P = sqrt(-4) assuming x=2, can u get a definite solution for it. No.
So, when we are given x<0, we have to take x as negative and then solve else we cant get answer in the choices mention and complex numbers are indeed out of scope of GMAT land.
I hope your confusion in cleared.....
Rajiv
What if i have not yet beat the beast, I know i will beat it!!!!!!!!
-
jimmiejaz
- Master | Next Rank: 500 Posts
- Posts: 207
- Joined: Sun Mar 11, 2007 6:16 pm
- Location: Mumbai
- Thanked: 11 times
if you are still confused, please post your detailed solution to this problem as to how are you solving this quetion. May be we can find an error in your approach which you are not able to spot.
Hope it helps
Hope it helps
What if i have not yet beat the beast, I know i will beat it!!!!!!!!
-
sushanta57021
- Junior | Next Rank: 30 Posts
- Posts: 22
- Joined: Mon Aug 11, 2008 10:35 am
- Thanked: 1 times
first of all there is a serious flaw in your explanation. see the highlighted text. i think you didn't get the point of my confusion.jimmiejaz wrote:Well, i understand your confusion.sushanta57021 wrote:sorry for posting it twice, but first i posted it in the wrong forum, i.e DS forum.
But anyway, I am not convinced with the answer yet.
We cann't take -X as answer only because X<0.
let me explain:
Say, P = [-X{abs(X)}]^1/2
is there any reason why P has to be positive? P can be negetive also, that means p can be X.
Can some one please clarify?
But, sqrt(-ve number) gives us a complex number.
Here we are given that x<0.
Lets go according to you,
P = sqrt(-4) assuming x=2, can u get a definite solution for it. No.
So, when we are given x<0, we have to take x as negative and then solve else we cant get answer in the choices mention and complex numbers are indeed out of scope of GMAT land.
I hope your confusion in cleared.....
Rajiv
i never considered P = sqrt(-4) assuming x=2
because i know X<0.
let me paraphrase the problem for your better understanding,
can you prove, [-X{abs(X)}]^1/2 >0, given x<0
then only we can get the answer.
anyway thanks for your effort, i really appreciate that, keep up your active participation.
and i could not solve the problem, for me answer can be either +X or -X
-
jimmiejaz
- Master | Next Rank: 500 Posts
- Posts: 207
- Joined: Sun Mar 11, 2007 6:16 pm
- Location: Mumbai
- Thanked: 11 times
we are given p = sqrt(-x|x|) where x<0
lets go by ur approach that soln is +x, it shall satisfy the equation.
p = sqrt(-x.x) since we took the solution as +x
p = sqrt(-x^2)
now, tell me how will you solve this as p = +x?
Hope you get the point now. That if we put the values and backsolve, only -x will give us answer. Hope it helps.
lets go by ur approach that soln is +x, it shall satisfy the equation.
p = sqrt(-x.x) since we took the solution as +x
p = sqrt(-x^2)
now, tell me how will you solve this as p = +x?
Hope you get the point now. That if we put the values and backsolve, only -x will give us answer. Hope it helps.
What if i have not yet beat the beast, I know i will beat it!!!!!!!!
-
sushanta57021
- Junior | Next Rank: 30 Posts
- Posts: 22
- Joined: Mon Aug 11, 2008 10:35 am
- Thanked: 1 times
No...your solution does not stand.jimmiejaz wrote:we are given p = sqrt(-x|x|) where x<0
lets go by ur approach that soln is +x, it shall satisfy the equation.
p = sqrt(-x.x) since we took the solution as +x
p = sqrt(-x^2)
now, tell me how will you solve this as p = +x?
Hope you get the point now. That if we put the values and backsolve, only -x will give us answer. Hope it helps.
I think i explained it earlier.
P = [-X{abs(X)}]^1/2
Say, X= -2, and can we not write:
(-2) = [-(-2){2}]^1/2
if this equation is true, then P can be X.
the highlighted area of your explanation is wrong.
solution is +X does not mean,
p = sqrt(-x.x), solution is +X only means P=+X,
the equation can still be written as
p = sqrt{-(-x).x}
which can give P as +X or -X.
