SOLUTION: Find the side length of a equilateral triangle with an area of 12 radical 3.

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Question 429889: Find the side length of a equilateral triangle with an area of 12 radical 3.
Found 3 solutions by Gogonati, poliphob3.14, richard1234:
Answer by Gogonati(855) About Me  (Show Source):
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Solution:Let x cm the side of equilateral triangle, then half of its perimeter will be: 3x/2 cm. If we apply Heron's Formula of triangle area, we have:
A=sqrt%28%28p-a%29%2A%28p-b%29%2A%28p-c%29%29, where p is half of perimeter and a=b=c=x cm the
sides of triangle.Substitute the given of our problem:
12sqrt%283%29=sqrt%28%28%283x%2F2%29-x%29%29%5E3, squaring both sides,
432=%28%283x%2F2%29-x%29%5E3
432=x%5E3%2F8,
x^3=432(8) => x=cubic root((432)(8)) => x=12(cubic root(2))cm
Done.

Answer by poliphob3.14(115) About Me  (Show Source):
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Solution:Apply Heron's Formula for equilateral triangle with side x xm have:
A=sqrt%28%283x%2F2%29%2A%283x%2F2-x%29%5E3%29, substituting our data we have:
12%2Asqrt%283%29=sqrt%28%283x%2F2%29%2A%28x%5E3%2F8%29%29, squaring both sides we have:
432=3x%5E4%2F16
6912=3x%5E4, divide by 3
2304=x%5E4, => x=fourth root of 2304 =>. Approximately x=7 cm.
Answer: The side of equilateral triangle with area 20.78 cm^2 is 6.93 cm.
Done.

Answer by richard1234(7193) About Me  (Show Source):
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One of the other tutors mis-applied Heron's formula. Instead of A+=+sqrt%28%28p-a%29%28p-b%29%28p-c%29%29, it is A+=+sqrt%28p%28p-a%29%28p-b%29%28p-c%29%29. Heron's formula works, but it is somewhat tedious. Also, we could use the standard A+=+bh%2F2 but that is boring, and there are faster solutions.

We can let the side length of the triangle be x. We can write the area in terms of two of the side lengths and the angle in between, i.e.

x%5E2%2Asin%2860%29%2F2+=+12sqrt%283%29

x%5E2%2Asin%2860%29+=+24sqrt%283%29. Since sin%2860%29+=+sqrt%283%29%2F2,

x%5E2%2Asqrt%283%29%2F2+=+24sqrt%283%29

x%5E2+=+48

x+=+sqrt%2848%29, approximately 6.928.