Question 200996
Remember,, equilateral  triangle,,  sides same,,,,
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Perimeter = sum  of  sides = s+s+s = 3s =12,,,,s=4
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With  s=3,  we  could  use  Herons  Formula  ,,  but  just  as  easy  to  resolve.
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Area  = 1/2 * base * height
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Height  is  perpendicular  to  base, therefore  c^2 = a^2 + b^2.( use  rough  sketch)
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in  our  case,,,c= 4,,,,a=2,,,,therefore  c= 3.46,,,which  is  height
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Area = 1/2 * 4 * 3.46 = 6.93
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Check,,,rough  sketch  shown  height to  vertex  makes  a  30-60-90 triangle, with  sides 1 - 2 - sqrt3,,
with  leg 2 and hypotenuse 4,  therefore other  leg  is 2(sqrt3) {height},
and  area  is  1/2 * 4* 2sqrt3 = 4 sqrt3 = 6.93,,,ok 
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