Question 652673
{{{drawing(400,320,-3,7,-3,5, graph(400,320,-3,7,-3,5), 

circle(0,0,2), triangle(-2,-2,-2,4,6,-2) )}}}
<pre>
The triangle it's inscribed in has nothing to do with it.  
The equation of any circle is

(x-h)² + (y-k)² = r²

You are given the center as (h,k) = {0,0}, the origin, and you are given
the radius r = 2, so

(x-0)² + (y-0)² = 2²

or

x² + y² = 4

Why was the triangle even mentioned?  It is totally irrelevant.

Edwin</pre>