If X<0, The sq root of (-XlXl) is what?
Was a bit confused when i saw this one, I though the sq root of a negative no. is not rational. Can some one help with the fundamentals on this one?
Thanks a lot
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GMAT Prep Questions
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Here is a print screen of the actual test, my answer was X but I was wrong. Answer is -X.
I have no idea how they come up with that answer.
I have no idea how they come up with that answer.
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Now that I know the answer, here is my explanation.
By definition,
|x| = x if x>0
-x if x<0
since x<0
sqrt( -x |x|) = sqrt( -x -x) = -x
but, I would have probably not thought of this before.
By definition,
|x| = x if x>0
-x if x<0
since x<0
sqrt( -x |x|) = sqrt( -x -x) = -x
but, I would have probably not thought of this before.
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I think this qs is some thing very tricky because the answer can be x as well as -x. Without knowing the answer before, we all may chose the answer - x. But now tell me how do u know that test-taker is looking for -x as x < 0. Because sqrt(-x|x|) = x or -x even if x < 0. God knows how to face this type of qs!
Correct me If I am wrong
Regards,
Amitava
Regards,
Amitava
- gabriel
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People we have had quite a lot of discussion on a similar problem some time back....
there is one very important thing to remember regarding square roots the Square root of a number is always positive
for eg. sqroot of 4 is 2... not 2 and -2 , 2 and -2 are the roots of the equation x^2-4=0, which simply means that 2 and -2 will both fulfill the above equation, but when we are talking about sqroot of a number it is always considered to be the positive root..
In the above question we have to find the sqroot(-Xmod(X)) where X<0 ...
Let X = -2, so we have to find the sqroot of (-(-2)mod(-2)) which is basically (2*2), so the square root is 2 .. but X = -2 therefore 2 = -X .. hence the answer is -X ...
Hope that helps ..
there is one very important thing to remember regarding square roots the Square root of a number is always positive
for eg. sqroot of 4 is 2... not 2 and -2 , 2 and -2 are the roots of the equation x^2-4=0, which simply means that 2 and -2 will both fulfill the above equation, but when we are talking about sqroot of a number it is always considered to be the positive root..
In the above question we have to find the sqroot(-Xmod(X)) where X<0 ...
Let X = -2, so we have to find the sqroot of (-(-2)mod(-2)) which is basically (2*2), so the square root is 2 .. but X = -2 therefore 2 = -X .. hence the answer is -X ...
Hope that helps ..
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gabriel, (thanks for sending me this link...)
Absolute value should be always positive...no?
your example is this (-(-2)mod(-2)) but I wonder it should be (-(-2)mod(2)) ??
Absolute value should be always positive...no?
your example is this (-(-2)mod(-2)) but I wonder it should be (-(-2)mod(2)) ??
- gabriel
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I think ur getting confused about what exactly is modulus of a number ..magical cook wrote:gabriel, (thanks for sending me this link...)
Absolute value should be always positive...no?
your example is this (-(-2)mod(-2)) but I wonder it should be (-(-2)mod(2)) ??
Let me just give a few examples
Mod(-2) = 2 and Mod(2)= 2 .. so what that means the mod of both -2 and 2 is the same ... 2 ..
in the question it says x is < 0 .. thats why the example of -2 ...
Does that help .. or am i misreading your query ?
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