Official GMATprep trial exam question 4

Jos wrote:

Can someone provide me with the rule for this one?

There's a nice rule that says √(xy) = (√x)(√y)
For example √(16*49) = (√16)(√49) = (4)(7) = 28

Since a² - b² = (a + b)(a - b), can use the above rule to conclude that...
its √[a² - b²] = √[(a+b)(a-b)] = [√(a+b)][√(a-b)] = D

Cheers,
Brent

Jos wrote:

Can someone provide me with the rule for this one?

Simplifying the given expression, we have:

√[(a + b)(a - b)] = √(a + b) x √(a - b)

Answer: D

Hi All,

This question has a great Geometry 'shortcut' built into it - but you have to recognize that the calculation is a variation on the Pythagorean Theorem (re: A^2 + B^2 = C^2). If you notice that, then you can TEST VALUES (using the classic 3/4/5 right triangle for the values). Here, that would be....

A = 5
B = 4
and the result of the calculation is 3. You'll find that only one answer matches...

Final Answer: [spoiler=]D[/spoiler]

GMAT assassins aren't born, they're made,
Rich