Square root +ve or -ve

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prachich1987: Legendary Member; Posts: 752; Joined: Sun Sep 12, 2010 2:47 amFollowed by: 10 members; Thanked: 20 times; GMAT Score:700

by prachich1987 » Thu Feb 03, 2011 3:59 am

If x^2 + y^2 =1, is x + y =1?
(1) xy =0
(2) y = 0

I am aware that the above question has been discussed earlier on the forum.
But I would like to know how to tackle with statement 2
Is it sufficient?

Thanks!
Prachi

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Source: Beat The GMAT — Data Sufficiency | Thu Feb 03, 2011 3:59 am

kmittal82: Master | Next Rank: 500 Posts; Posts: 324; Joined: Mon Jul 05, 2010 6:44 amFollowed by: 3 members; Location: London; Thanked: 70 times

by kmittal82 » Thu Feb 03, 2011 4:05 am

Looking at 2:

y = 0, this means x^2 = 1, wihch means x could be +1 or -1

Now, if x = +1, x + y = 1, whereas if x = -1, x + y = -1

So, statement 2 raises ambiguity, hence not sufficient

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prachich1987: Legendary Member; Posts: 752; Joined: Sun Sep 12, 2010 2:47 amFollowed by: 10 members; Thanked: 20 times; GMAT Score:700

by prachich1987 » Thu Feb 03, 2011 4:11 am

kmittal82 wrote:Looking at 2:

y = 0, this means x^2 = 1, wihch means x could be +1 or -1

Now, if x = +1, x + y = 1, whereas if x = -1, x + y = -1

So, statement 2 raises ambiguity, hence not sufficient

Thanks !
I have one more question.
On GMAT, can the square root of 4 be both +2 and -2
I remember there is some rule related to square roots.
But I am not able to recall it.I think I need to take a break :roll:

Last edited by prachich1987 on Thu Feb 03, 2011 7:41 am, edited 1 time in total.

Thanks!
Prachi

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kmittal82: Master | Next Rank: 500 Posts; Posts: 324; Joined: Mon Jul 05, 2010 6:44 amFollowed by: 3 members; Location: London; Thanked: 70 times

by kmittal82 » Thu Feb 03, 2011 4:17 am

prachich1987 wrote:
kmittal82 wrote:Looking at 2:

y = 0, this means x^2 = 1, wihch means x could be +1 or -1

Now, if x = +1, x + y = 1, whereas if x = -1, x + y = -1

So, statement 2 raises ambiguity, hence not sufficient
Thanks !
I have one more question.
On GMAT, can the square root of 4 be both +2 and -2
I remember there is some related to it square roots.
But I am not able to recall it.I think I need to take a break :roll:

I would go as far as saying you can bet on the fact GMAT will exploit the fact that sqrt(4) can be +2 or - 2

Speaking of breaks, now is a good time for me to do some work... the kinds I get paid to do

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Geva@EconomistGMAT: GMAT Instructor; Posts: 905; Joined: Sun Sep 12, 2010 1:38 amFollowed by: 123 members; Thanked: 378 times; GMAT Score:760

by Geva@EconomistGMAT » Thu Feb 03, 2011 7:32 am

prachich1987 wrote:
kmittal82 wrote:Looking at 2:

y = 0, this means x^2 = 1, wihch means x could be +1 or -1

Now, if x = +1, x + y = 1, whereas if x = -1, x + y = -1

So, statement 2 raises ambiguity, hence not sufficient
Thanks !
I have one more question.
On GMAT, can the square root of 4 be both +2 and -2
I remember there is some related to it square roots.
But I am not able to recall it.I think I need to take a break :roll:

According to the official guide page 114, the sqrt of 4 (or any number) is only the positive root: âˆš4=2, not Â±2.

However, x^2=1 is not the same thing: it is a quadratic equation with x, which can have more than one solution - both x=1 and x=-1 will satisfy the equation x^2=1, and so x could equal either of these solutions.

Draw the distinction between roots of numbers (only the positive root) and roots of variables (in which case you need to look at all possible solutions that satisfy the equation).

Geva
Senior Instructor
Master GMAT
1-888-780-GMAT
https://www.mastergmat.com

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prachich1987: Legendary Member; Posts: 752; Joined: Sun Sep 12, 2010 2:47 amFollowed by: 10 members; Thanked: 20 times; GMAT Score:700

by prachich1987 » Thu Feb 03, 2011 7:43 am

Thanks Geva!!!

Thanks!
Prachi

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