The two sides of a right triangle are 5cm and 8.4cm respectively, what is its area in cm**2.
直角三角形两条直角边分别是5cm和8.4cm，它的面积是多少cm**2．
<gadget id="calculator">8.4 / 2</gadget>
<output>4.2</output>

<gadget id="calculator">5 * 4.2</gadget>
<output>21</output>

<result>21</result>