(1/11+1/21+1/31+1/41)*(1/21+1/31+1/41+1/51)-(1/11+1/21+1/31+1/41+/51)*(1/21+1/31+1/41)

问题描述:

(1/11+1/21+1/31+1/41)*(1/21+1/31+1/41+1/51)-(1/11+1/21+1/31+1/41+/51)*(1/21+1/31+1/41)

(1/11+1/21+1/31+1/41)*(1/21+1/31+1/41+1/51)-(1/11+1/21+1/31+1/41+/51)*(1/21+1/31+1/41)
=【1/11+(1/21+1/31+1/41)】*(1/21+1/31+1/41+1/51)-【1/11+(1/21+1/31+1/41+/51)】*(1/21+1/31+1/41)
=1/11*(1/21+1/31+1/41+1/51)+(1/21+1/31+1/41)(1/21+1/31+1/41+1/51)-1/11*(1/21+1/31+1/41)-(1/21+1/31+1/41)*(1/21+1/31+1/41+1/51)
=1/11*(1/51)=1/561