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Official GMATprep trial exam question 4

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by Brent@GMATPrepNow » Mon Oct 30, 2017 8:30 am
Jos wrote:Image

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

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by Scott@TargetTestPrep » Thu Nov 07, 2019 6:39 pm
Jos wrote:Image

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

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by [email protected] » Sun Nov 24, 2019 11:34 am
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]

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