(1+(1/2))*(1-(1/2))*(1+(1/3))*(1-(1/3))*...*(1+(1/9) )*(1-(1/9))=how much.
(1+(1/2))*(1-(1/2))*(1+(1/3))*(1-(1/3))*…*(1+(1/9))*(1-(1/9))=多少．
<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">10 / 9</gadget>
<output>10/9 = around 1.111111</output>

<gadget id="calculator">(1/2) * (10/9)</gadget>
<output>5/9 = around 0.555556</output>

<result>5/9 = around 0.555556</result>