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Question
A traffic signal board, indicating ‘SCHOOL AHEAD’, is an equilateral triangle with side ‘a’. Find the area of the signal board, using Heron’s formula. If its perimeter is 180 cm, what will be the area of the signal board?
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Solution
The side of the traffic signal board = a
Perimeter of traffic signal board = 3 × a
2s = 3a ⇒ s = `3/2 a`
By heron's formula,
Area of triangle = `sqrt(s(s-a)(s-b)(s-c))`
Area of given triangle = `sqrt(3/2 a(3/2a-a)(3/2a-a)(3/2a-a))`
= `sqrt((3/2a)(a/2)(a/2)(a/2))`
= `sqrt3/4a^2` ... (1)
Perimeter of traffic signal board = 180 cm
Side of traffic signal board (a) = `(180/3) cm` = 60 cm
Using equation (1), the area of the traffic signal board
= `sqrt3/4(60cm)^2`
= `(3600/4sqrt3)cm^2` = `900sqrt3 cm^2`
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