Area of Equilateral Triangle with Inradius R

CMAT 2023 · Quantitative Techniques & Data Interpretation · Easy · Geometry

What is the area of an equilateral triangle whose inscribed circle has radius R?

  1. A.

    4R24R^2

  2. B.

    43R24\sqrt{3}R^2

  3. C.

    (3+22)R2(3 + 2\sqrt{2})R^2

  4. D.

    33R23\sqrt{3}R^2

Answer

D

Explanation

For an equilateral triangle of side aa, inradius r=R=a23⇒a=23Rr = R = \frac{a}{2\sqrt{3}} \Rightarrow a = 2\sqrt{3}R. Area = 34a2=34(23R)2=34(12R2)=33R2\frac{\sqrt{3}}{4} a^2 = \frac{\sqrt{3}}{4} (2\sqrt{3}R)^2 = \frac{\sqrt{3}}{4} (12R^2) = 3\sqrt{3}R^2.

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