What is the area of a sector with a radius of 2 cm and a central angle of 90 degrees?
一个半径2厘米，圆心角是90度的扇形面积是多少．
<gadget id="calculator">90 / 360</gadget>
<output>1/4 = around 0.25</output>

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

<gadget id="calculator">(1/4) * 3.14 * 4</gadget>
<output>3.14</output>

<result>3.14</result>