comma884
幼苗
共回答了17个问题采纳率:94.1% 举报
=(1/37+1/41+1/43+1/47+1/53)*(1/41+1/43+1/47+1/53)+(1/37+1/41+1/43+1/47+1/53)*(1/54)-(1/37+1/41+1/43+1/47+1/53)*(1/41+1/43+1/47+1/53)-(1/54)*(1/41+1/43+1/47+1/53)
=(1/37+1/41+1/43+1/47+1/53)*(1/54)-(1/54)*(1/41+1/43+1/47+1/53)
=(1/54)*(1/37)
=1/1998
1年前
4