math
posted by Leasha .
An equilateral triangle is inscribed in a circle. The radius of the circle is 21 in. Determine the side length of the triangle to the nearest 10th of an inch

3 isosceles triangles around circle center with equal legs of 21 in and included angle of 360/3 = 120 degrees
other 2 angles are (180120)/2 = 30 deg
law of sines
sin 120/base = sin 30/21
.866/base = .5/21
so base, which is a side of our triangle = .866 *21 * 2 = 36.4 in 
Thanks so much!