Calculation: (1/2)-(1/6)-(1/12)-(1/20)-...-(1/90).
计算：(1/2)-(1/6)-(1/12)-(1/20)-…-(1/90)．
<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">1 / 9</gadget>
<output>1/9 = around 0.111111</output>

<gadget id="calculator">(1/2) - (1/9)</gadget>
<output>7/18 = around 0.388889</output>

<gadget id="calculator">(1/2) - (7/18)</gadget>
<output>1/9 = around 0.111111</output>

<result>1/9 = around 0.111111</result>