Question 985461
The points X(3,4) and Y(9,1) lie on the circumference of a circle.  There is exactly 60 degree of arc between X and Y. Find the radius of the circle.
<pre>Line segment XY = {{{3*sqrt(5)}}}
With center O, radii OX and OY are congruent
With arc XY being {{{60^o}}}, central angle XOY also equals {{{60^o}}}
With radii OX and OY congruent, an equilateral triangle is formed
With line segment XY being {{{3*sqrt(5)}}}, radii also measure: {{{highlight_green(3*sqrt(5))}}}