When a = 20 cm, h = 9 cm, the area of the triangle S = how many square centimeters.
当a=20厘米，h=9厘米时，三角形面积S=多少平方厘米．
<gadget id="calculator">9 / 2</gadget>
<output>9/2 = around 4.5</output>

<gadget id="calculator">20 * (9/2)</gadget>
<output>90</output>

<result>90</result>