Perimeter and Area of an Equilateral Triangle

Geometry Level 1

The area of an equilateral triangle is 25 3 25\sqrt{3} square rods. What is it’s perimeter in rods?

24 27 30 33

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3 solutions

Mahdi Raza
Jun 13, 2020

Let s s be the side of the equilateral triangle, then:

3 4 s 2 = 25 3 3 s 2 = 25 3 4 s 2 = 100 s = 10 \begin{aligned} \dfrac{\sqrt{3}}{4}s^2 &= 25\sqrt{3} \\ \cancel{\sqrt{3}}s^2 &= 25\cancel{\sqrt{3}} \cdot 4 \\ s^2 &= 100 \\ \implies s &= 10 \end{aligned}

Perimeter of an equilateral triangle is 3 s = 3 ( 10 ) = 30 3s = 3(10) = \boxed{30}

The formula for the area of an equilateral triangle is A = 3 4 x 2 A=\dfrac{\sqrt{3}}{4}x^2 where x x is the side length. We have

25 3 = 3 4 x 2 25\sqrt{3}=\dfrac{\sqrt{3}}{4}x^2

100 = x 2 100=x^2

10 = x 10=x

So the desired perimeter is

P = 3 x = 3 ( 10 ) = 30 r o d s P=3x=3(10)=\color{#69047E}\boxed{30~rods}

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