GMAT PREP Square Roots

[Viswanathan.harsha]

If X<0, then Sqrt (-X *abs(X)) is:

A.) -X
B.) -1
C.) 1
D.) X
E.) Sqrt (X)


Can someone please help me with this?





THE OA is A

[parthatayi]

If X<0, then Sqrt (-X *abs(X)) is:

A.) -X
B.) -1
C.) 1
D.) X
E.) Sqrt (X)


Can someone please help me with this?





THE OA is A

Hi Vishwanath,

The expression under the square root would be x^2.
and square root of x^2 is mod(x).
As x <0 => the value is -x.

Thanks and Regards,
Partha

[Viswanathan.harsha]

Thanks for the explanation. Can you please explain what you mean by mod (X) ?

[parthatayi]

Thanks for the explanation. Can you please explain what you mean by mod (X) ?

mod(x) is nothing but modulus of x.

Thanks and Regards,
Partha.

[Viswanathan.harsha]

Thanks, i've been using abs(x) for so long that I forgot about the term Mod(x). I guess since the mod(x) must be a positive number, and x < 0, then to make the over value positive, it must be (-X) = X. Is this correct?

[parthatayi]

Thanks, i've been using abs(x) for so long that I forgot about the term Mod(x). I guess since the mod(x) must be a positive number, and x < 0, then to make the over value positive, it must be (-X) = X. Is this correct?

The definition of mod(x) is as follows:
y=|x|
y=x if x>0
y= -x if x<0

Hence in our question its given that x<0
=> ans is -x

Thanks and Regards,
Partha.

[RonPurewal]

by far the easiest way to solve this problem is to pick your own number for x.
the prompt implies that this will work for all values of x < 0, so it's guaranteed that you'll be able to pick any such value.

let's say x = -4.
then the prompt becomes √(-(-4)(4)), or √16 = 4.
(a) 4
(b) -1
(c) 1
(d) -4
(e) impossible

done. answer (a).