Question 1152915
<pre>
The equation for an ellipse is
{{{ x^2/a^2 + y^2/b^2 = 1 }}}

If a=b then this reduces to:
{{{ x^2/a^2 + y^2/a^2 = 1 }}}

and by multiplying both sides by a^2
{{{ x^2 + y^2 = a^2 }}}

You should recognize this as the equation of a circle with radius a.