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Bunuel
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Active GMAT Club Expert! Tag them with @ followed by their username for a faster response.
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nicbo
Hey gmatophobia thank you for your explanation! I have two questions:

How do you get the 2/√3 in the first step?

And why do multiply by √3 in the third step?

Thank you in advance!

nicbo - Here are the responses to your queries -

Quote:
How do you get the 2/√3 in the first step?

In \(\triangle ABD \)

  • \(\angle ABD = 60\)
  • \(\angle ADB = 90\)
  • \(\angle BAD = 30\)

Hence, the sides are on a fixed ration

\(BD : AD : AB = 1 : \sqrt{3} : 2\)

The question stem provides us with the value of AD. Hence to find the value of AB, we have to multiply by\( \frac{2}{\sqrt{3}}\)

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And why do multiply by √3 in the third step?

We had to multiply both the numerator and denominator by \(\sqrt{3}\) to rationalize the denominator. Note, in none of the answers presented, we have \(\sqrt{3}\) , hence to remove the same, we had to multiply both the numerator and denominator by \(\sqrt{3}\) .
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let's call each side X
\(\frac{AD}{BC}=12\)
\(\frac{AD}{x}=12\)

AD=12x

also the formula for height of an equilateral triangle is ((side)^2 sqrt3)/2

\(12x=\frac{x^2\sqrt{3}}{2}\\
24x=x^2\sqrt{3}\)

\(24=x\sqrt{3}\) rationalize by \(\sqrt{3}\)

\(\frac{24}{\sqrt{3}}=x\)

IMO A


\(\frac{24\sqrt{3}}{3}\)
\(=8\sqrt{3}\)
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