GMAT PREP 1 - PS

[moadhia]

Can anyone help me solve this? I dont understand mod sign there. Whats the logic behind that ??

[gmat740]

Square root of a number is always +/-

eg: square root of 4= 4^0.5 = +2 and -2

so sq-rt(x^2) has to be +x and -x

and |x| = +x when x>0 and -x when x<0

so E is clearly an answer

Hope it helps

[moadhia]

so if the questions stated that X >0, the ans would have been 1 or if X<0 , ans would have been -1 ??

[gmat740]

yes exactly

But it has to be mentioned otherwise we cannot assume something like that.

[bluementor]

Square root of a number is always +/-

eg: square root of 4= 4^0.5 = +2 and -2

so sq-rt(x^2) has to be +x and -x

This is not true. the square root function will only return a positive value (or zero).

So &#8730;(x^2) = |x|, and thats why the answer is E.

-BM-

[gmat740]

The number inside a square root is always positive(otherwise we will have complex roots, i or w etc if you are from engineering background you will be knowing about this )

However,

The number we get after taking a square root can be positive as well as negative

You need to check it again BM

regards

Karan

[bluementor]

The number inside a square root is always positive(otherwise we will have complex roots, i or w etc if you are from engineering background you will be knowing about this )

However,

The number we get after taking a square root can be positive as well as negative

You need to check it again BM

regards

Karan

Karan, have a look at the explanation by Ian in this post:

https://www.beatthegmat.com/difference-b ... 12863.html

-BM-

[gmat740]

BM,
I just saw the post you referred to, and I wonder,Is the GMAT maths different from the fundamental Maths which we learn in our school!!

I don't know how many times basic fundamental rules change in GMAT,but may be like this I am going to have a very low score because I don't take any tutorials for GMAT,considering that GMAT follows the same fundamental rules of maths as followed elsewhere, but seems like I am making a mistake

Thanks For Pointing me

Karan