Question 1141841
.
<pre>
The equation


    {{{(x-h)^2}}} + {{{(y-k)^2}}} = a


with  a >= 0  represents the circle in (x,y) plane with the center at the point (h,k) and the radius of  {{{sqrt(a)}}}.



It is written in any textbook, and you should memorize it as  "2 x 2 = 4".
</pre>