If the two sides of a right triangle are 20 cm and 30 cm respectively, what is its area in square centimeters?
一个直角三角形的两条直角边分别是20厘米，30厘米，它的面积是多少平方厘米．
<gadget id="calculator">30 / 2</gadget>
<output>15</output>

<gadget id="calculator">20 * 15</gadget>
<output>300</output>

<result>300</result>