Squaring

[medea66]

I picked numbers for this one(perfect squares), but I guess not the right numbers since they don't work out with the given solution.......

[sudhir3127]

Plug in the values...
i took a=2 and b =1

hence sqroot(a^2-b^2) = sqrt(2^2-1^2)=sqrt(3)

only option D gives me sqrt(3).

hope it helps..

[bluementor]

I'm not sure if my approach would be ideal for other similar questions, but here it goes:

sqrt(a^2 - b^2)
= sqrt((a-b)(a+b))
= sqrt(a-b)*sqrt(a+b)

BlueMentor

[santa_dem]

Just remember that x^2-y^2=(x+y)*(x-y).

Simple as that.

[medea66]

I think the mistake I made is that I felt compelled to pick perfect squares for A & B, and in the process I complicated the calculation.

The calculation is alot simpler if I pick just 1 & 2 for A & B, respectively.

[Ian Stewart]

Just remember that x^2-y^2=(x+y)*(x-y).

Simple as that.

Exactly. You will see a difference of squares on your GMAT, guaranteed. Be sure you can recognize it, and factor it when it shows up. If you notice, in this question, that the expression under the root is a difference of squares, the problem is straightforward- much faster than choosing numbers.