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First term is positive, second term is negative, third term is positive.

Only one negative answer.

D

you think like me . that's a gmat solution right there.

what if all the choices were negative. ..just for the sake of discussion

2

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_________________

Best,

AkamaiBrah Former Senior Instructor, Manhattan GMAT and VeritasPrep Vice President, Midtown NYC Investment Bank, Structured Finance IT MFE, Haas School of Business, UC Berkeley, Class of 2005 MBA, Anderson School of Management, UCLA, Class of 1993

Did the others, including me ignore the negative value of the sqrt root here?

Example

4 + sqrt (16) ....this would be 8 isnt it?

but sqrt(16) = - 4 too...

Do we always take the positive value of the sqrt root in "expressions", unless otherwise mentioned.

thanks praetorian

In the gmat, the square root sign signifies positive square root. HOWEVER, since I squared an expression in one of the steps in my solution, I no longer can claim the square root to be positive, i.e., I cannot say if x = -2 I cannot say since x^2 = 4, x = sqrt(x^2) = 2.

Going back to my solution, I would have to notice that the answer must be negative, then choose the correct root.
_________________

Best,

AkamaiBrah Former Senior Instructor, Manhattan GMAT and VeritasPrep Vice President, Midtown NYC Investment Bank, Structured Finance IT MFE, Haas School of Business, UC Berkeley, Class of 2005 MBA, Anderson School of Management, UCLA, Class of 1993

The value of (4+sqrt15) * (sqrt6-sqrt10) * sqrt(4-sqrt15) = x
x * sqrt(4-sqrt15) = (4+sqrt15) * (sqrt6-sqrt10) * (4-sqrt15)
= (16-15) * ( sqrt6-sqrt10 )

now squaring both sides we get
sqr(x) * ( 4-sqrt15 ) = 6+10-2 * sqr(6*10)

sqr(x) = 4 so x = +-2
x cannot be +ve because sqrt(4-sqrt15) is +ve and
(sqrt6-sqrt10) is -ve. Just from this we should be able to conclude that the answer is -ve