Question 1191157
<pre>
{{{drawing(400,400,-1.5,1.5,-1.5,1.5,
locate(-.33,.34,r),
circle(0,0,1),locate(-.1,.25,110^o),locate(0,.7,18),
triangle(.8191520443,.5735764364,-.8191520443, .5735764364,0,0) )}}}

Split the triangle into two congruent right triangles:

{{{drawing(400,400,-1.5,1.5,-1.5,1.5,
line(0,0,0,.5735764364),  locate(-.33,.34,r),
circle(0,0,1),locate(-.21,.32,55^o),locate(-.38,.7,9),


triangle(.8191520443,.5735764364,-.8191520443, .5735764364,0,0) )}}}

{{{sin(55^o)=opposite/hypotenuse=9/r}}}

You finish by solving that for r.

Edwin</pre>