Question 1112131
.
The area of a regular triangle equals 


{{{S}}} = {{{3}}}.{{{R^2}}}.cos(60°).sin(60°) = {{{3}}}.{{{R^2}}}.{{{1/2}}}.{{{sqrt(3)/2}}} = {{{3sqrt(3)/4}}}{{{R^2}}}, 


where  {{{R}}}  is the radius of the circumscribed circle. 



See the lesson 

&nbsp;&nbsp;&nbsp;&nbsp;- <A HREF=https://www.algebra.com/algebra/homework/Surface-area/Area-of-a-regular-n-sided-polygon-via-the-radius-of-the-circumscribed-circle.lesson?content_action=edit_dev>Area of a regular n-sided polygon via the radius of the circumscribed circle</A>, Example 1

in this site.


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