gmat prep ps modules

[replayyyy]

If x<0, then second square of -x*|x| is

-x
-1
0
x
second square of x

[diebeatsthegmat]

If x<0, then second square of -x*|x| is

-x
-1
0
x
second square of x

is second square meant squareroot?

because x is negative |x|=-x and -(-x)=x so the second suare of x*-x=-x
the answer is A

[replayyyy]

If x<0, then second square of -x*|x| is

-x
-1
0
x
second square of x

is second square meant squareroot?

because x is negative |x|=-x and -(-x)=x so the second suare of x*-x=-x
the answer is A

yes, it is squareroot, my mistake

[rkanthilal]

I'm getting D for this one.

If X<0

-(-x)*|x|=x^2
sqrt x^2 = x

[gtestprep]

I'm getting D for this one.

If X<0

-(-x)*|x|=x^2
sqrt x^2 = x

Yep. That's right, if x < 0 then |x| = - x. So the equation becomes -x * -x = x ^2
The square-root of x^2 = +x

[diebeatsthegmat]

I'm getting D for this one.

If X<0

-(-x)*|x|=x^2
sqrt x^2 = x

Yep. That's right, if x < 0 then |x| = - x. So the equation becomes -x * -x = x ^2
The square-root of x^2 = +x

you guys forget a negative mark... its squareroot of (-x)|x|
so solve the (-x) first : if x is negative so (-x) will be [-(-x)]=x
x<0 so |x|=-x
so squareroot of (-x)x=-square root of x^2=-x
the answer must be A

[rkanthilal]

I'm getting D for this one.

If X<0

-(-x)*|x|=x^2
sqrt x^2 = x

Yep. That's right, if x < 0 then |x| = - x. So the equation becomes -x * -x = x ^2
The square-root of x^2 = +x

you guys forget a negative mark... its squareroot of (-x)|x|
so solve the (-x) first : if x is negative so (-x) will be [-(-x)]=x
x<0 so |x|=-x
so squareroot of (-x)x=-square root of x^2=-x
the answer must be A

You are correct. The answer is A.

For example, if x=-2
sqrt(-x*|x|)=sqrt(-(-2)*|-2|)=sqrt(2*2)=2

[rros0770]

Confused slightly here. rkanthilal, you proved the answer to be (D) which is x


Hey Die, I'm looking at your explanation:
you guys forget a negative mark... its squareroot of (-x)|x|
so solve the (-x) first : if x is negative so (-x) will be [-(-x)]=x
x<0 so |x|=-x


Wouldnt the value of Absolute (x) be the positive value of (x), being that absolute value is essentially the distance between a given number and zero ? For example:

|3|= 3
|-4|= 4

so, being that we know (X) is negative, the absolute value would make it a positive. Essentially we'd get end up with 2 positive values for (X), and the sqroot root would leave us with choice D which is (X)


Just wanted to clarify, am I missing some sort of principle or rule here?

[diebeatsthegmat]

I'm getting D for this one.

If X<0

-(-x)*|x|=x^2
sqrt x^2 = x

Yep. That's right, if x < 0 then |x| = - x. So the equation becomes -x * -x = x ^2
The square-root of x^2 = +x

you guys forget a negative mark... its squareroot of (-x)|x|
so solve the (-x) first : if x is negative so (-x) will be [-(-x)]=x
x<0 so |x|=-x
so squareroot of (-x)x=-square root of x^2=-x
the answer must be A

well, if its a real number for x such as x= 2 or -2
things will be different, the answer, i meant... so yes, you
You are correct. The answer is A.

For example, if x=-2
sqrt(-x*|x|)=sqrt(-(-2)*|-2|)=sqrt(2*2)=2

well, if its a real number for x such as x= 2 or -2
things will be different, the answer, i meant will be different, the answer will be always a positive number for any real negative/positive number,,,

[rkanthilal]

rros0770, I think you are making the same error that I originally did. Yes, since X<0 when we multiply -x and |x| we are multiplying two positive numbers. Then when we take the sqrt of that number we end up with another positive number.

If (D) is correct and the answer is X, then that would mean the result is negative (since x is a negative number). I think the confusion is because we are giving the answer in terms of X. Substitute an actual number and it becomes clearer.

For example, if x=-2
sqrt-x*|x|
sqrt-(-2)*|-2|
sqrt(2*2)=2

Here x=-2. The result of the equation is positive 2. If we are to give the result in terms of x, the answer is -x (since x is negative).

Hope that helps...

[fskilnik@GMATH]

If x<0, the square root of -x*|x| is

-x
-1
0
x
second square of x

Hi guys,

Let me show you how to "deal" with absolute values (modulus) without "suffering"...

From the fact that x is negative, we know that |x| = -x (and please note that here "- x" is the opposite of a negative number, therefore here we are sure "- x" is POSITIVE).

Therefore -x |x| = -x (-x) = x^2 and finally, remembering that: sqrt (x^2) = |x| we have (in this case) that sqrt(x^2) = |x| = -x, and we are done.

Regards,
Fabio.