rk9 wrote:

So I ran across this question in the GMAT paper exams:

What is the value of a - b?

(1) a = b + 4

(2) (a - b)^2 = 16

I marked D since I thought that the GMAT only considers square roots of numbers to equal the positive root only and not the negative root. Thus, wouldn't (2) above be equivalent to a - b = 4? Can someone please explain to me how the GMAT treats square roots of numbers? Thanks!

You are right +ve square roots are there. But when you will take square root on both the sides, how you will come to know whether a>b or b>a

(a - b)^2 = 16 take square root on both the sides

=> |a-b| = 4 , see both the square roots are positive. Now when you will open the modulus you will have to consider two cases.

a>b and b>a

if a>b then a - b = 4

if b>a then a - b = -4.

Hope this helps

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