If you define a△b=2ab-b**2, then 7△9=how many
如果定义a△b=2ab-b**2，那么7△9=多少
<gadget id="calculator">2 * 7 * 9</gadget>
<output>126</output>

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

<gadget id="calculator">126 - 81</gadget>
<output>45</output>

<result>45</result>