Properties of TriangleHard
Question
Let a point A lie between the parallel lines $L_{1}$ and $L_{2}$ such that its distances from $L_{1}$ and $L_{2}$ are 6 and 3 units, respectively. Then the area (in sq. units) of the equilateral triangle ABC, where the points B and C lie on the lines $L_{1}$ and $L_{2}$ respectively, is :
Options
A.$15\sqrt{6}$
B.27
C.$21\sqrt{3}$
D.$12\sqrt{2}$
Solution
Sol.
$${sin\theta = \frac{3}{a} }{sin\left( 60^{\circ} + \theta \right) = \frac{9}{a} }{\frac{\sqrt{3}}{2}cos\theta + \frac{1}{2}sin\theta = \frac{9}{a} }{\sqrt{3}\sqrt{1 - \frac{9}{a^{2}}} + \frac{3}{a} = \frac{18}{a} }{a = \sqrt{84} }$$Area of $\bigtriangleup ABC = \frac{\sqrt{3}}{4}a^{2} = \frac{\sqrt{3}}{4} \times 84 = 21\sqrt{3}$
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