(1/(a))+(1/(b))=1, (1/(a))+(1/(b))+(1/(c))=2.7(a, b, c are all is not 0), then c=how much.
(1/(a))+(1/(b))=1，(1/(a))+(1/(b))+(1/(c))=2.7(a，b，c均不为0)，则c=多少．
<gadget id="calculator">1 / 1.7</gadget>
<output>0.588235</output>

<result>0.588235</result>