What is the area of a semicircle with a radius of 2 cm in square centimeters?
半径为2厘米的半圆的面积是多少平方厘米．
<gadget id="calculator">2 ** 2</gadget>
<output>4</output>

<gadget id="calculator">4 / 2</gadget>
<output>2</output>

<gadget id="calculator">3.14 * 2</gadget>
<output>6.28</output>

<result>6.28</result>