Question 480322
<pre>
{{{A=pi*r^2}}}

The radius r is {{{1/2}}} the diameter, which is 21,
so the radius r = {{{expr(1/2)21=21/2}}}

{{{A=pi*(21/2)^2}}}

{{{A=pi*(21^2/2^2)}}}

{{{A=pi*(441/4)}}}

{{{A=(pi/1)*(441/4)}}}


{{{A=441pi/4}}}

</pre>