Equilateral Triangle Perpendiculars

CAT 2020 Slot 2 · Quantitative Ability · Hard · Geometry

This is a hard Quantitative Ability question from the CAT 2020 Slot 2 paper. It tests Geometry. The full answer key and a step-by-step explanation are below — try it yourself first, then reveal the solution.

From the interior point of an equilateral triangle, perpendiculars are drawn on all three sides. The sum of the lengths of the perpendiculars is ss. Then the area of the triangle is

  1. A.

    \frac{s^2}{2\sqrt{3}}

  2. B.

    \frac{2s^2}{\sqrt{3}}

  3. C.

    \frac{s^2}{\sqrt{3}}

  4. D.

    \frac{\sqrt{3}s^2}{2}

Answer

C

Explanation

For an equilateral triangle of side aa, the sum of perpendicular distances p1+p2+p3p_1 + p_2 + p_3 from any interior point to the sides is equal to the altitude hh of the triangle. Thus, h=sh = s. Since height of an equilateral triangle is h=32ah = \frac{\sqrt{3}}{2} a, we have a=2s3a = \frac{2s}{\sqrt{3}}. The area of the equilateral triangle is: Area=34a2=34(2s3)2=344s23=s23\text{Area} = \frac{\sqrt{3}}{4} a^2 = \frac{\sqrt{3}}{4} \left(\frac{2s}{\sqrt{3}}\right)^2 = \frac{\sqrt{3}}{4} \cdot \frac{4s^2}{3} = \frac{s^2}{\sqrt{3}}

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