If there is a right triangle with angles of 45 degrees and the longest side is 18 centimeters, what is its area in square centimetres?
有一个角为45度的直角三角形，最长边是18厘米，那么它的面积是多少平方厘米
<gadget id="calculator">18 / 2</gadget>
<output>9</output>

<gadget id="calculator">9 / 2</gadget>
<output>9/2 = around 4.5</output>

<gadget id="calculator">18 * (9/2)</gadget>
<output>81</output>

<result>81</result>