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Ps set 11 q 7


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If x

A) -x

B) -1

C) 1

D) x

E) sqrt(x)

 

A quick way to solve this question is to plug in a value for x.

Since x

 

So, the sqrt[-x (|x|)] = sqrt[5 (|-5|)] = sqrt[5(5)] = sqrt[25] = 5

 

Answer choice A is -x, so if x= -5, then -x = 5. Since our output above is 5, answer choice A is correct.

 

Cheers,

Brent

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What we are finding here ? sqrt (- x.|x|) = ? right ?.

As x is negative - x is supposed to be positive . That means X. Besides, | - x| = x.

so sqrt (-x.|x|)= sqrt (x.x) = sqrt (x^2) = x. The option is D.

 

Please point out the my mistake.

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Hey 800, You have presupposed that x is negative, i.e -x and you are calculation leads to x, which is positive in sign. Hence you need -(-x )....

 

Even simpler, lets assume, x to be -y , you have SQRT ( -(-y) . | -y | ) = SQRT (y^2 ) = Y.... But what is y ??? -x..... Hence answer is A.

 

Thanks Brent for the explanation.

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Hey 800, You have presupposed that x is negative, i.e -x and you are calculation leads to x, which is positive in sign. Hence you need -(-x )....

 

Even simpler, lets assume, x to be -y , you have SQRT ( -(-y) . | -y | ) = SQRT (y^2 ) = Y.... But what is y ??? -x..... Hence answer is A.

 

Thanks Brent for the explanation.

 

No. But I have calculated x with negative sign. Why should I add another negative sign after calculation. Please explain. I think in G-day I will commit same mistake if I am not clear.

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Yes I got the point !!! I missed the basic of roots!

Rule: a root can only have a negative value if 1. it is an odd root and 2. the base of the root is negative. Here I had to apply the second condition of the rule.

Thanks Brent & shyamprasadrao to inspire me to review the basic.

 

Cheers !!!

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