Lesson: “Fixing” the Denominator

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I think rather than using FOIL method, I'd use algebraic identity (a+b)(a-b) = a^2-b^2. It might save a second or two when dealing with conjugates.
gmat-admin's picture

I totally agree that that would save time.
I don't mention the Difference of Squares approach (found here https://www.gmatprepnow.com/module/gmat-algebra-and-equation-solving/vid...), because many students follow the course as it's laid out in the Learning Guide, and those students haven't covered that lesson yet.

For the second question, why aren't we multiplying 3 X root 25, which is 5, to get 2 root 50 in the numerator and 15 in the denominator? Thanks!
gmat-admin's picture

That's totally valid. However, once we get to (2√50)/15, we need to recognize that we can simplify this fraction further, since √50 = √(25 x 2) = √25 x √2 = 5√2

So, (2√50)/15 = 2(5√2)/15 = 2√2/3

Reinforcement activity #3 (counting top-to-bottom) from Veritas Prep is the same as #4 from GMAT Club.
gmat-admin's picture

Good catch - thanks!
I have removed one of the duplicate links.


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