(1+1/16+1/17+1/18)×(1/16+1/17+1/18+1/19)-(1+1/16+1/17+1/18+1/19)×(1/16+1/17+1/18)=

问题描述:

(1+1/16+1/17+1/18)×(1/16+1/17+1/18+1/19)-(1+1/16+1/17+1/18+1/19)×(1/16+1/17+1/18)=

=[(1+1/16+1/17+1/18)*(1/16+1/17+1/18)+(1+1/16+1/17+1/18)*1/19)]-[(1+1/16+1/17+1/18)*(1/16+1/17+1/18)+(1/19*(1/16+1/17+1/18))]=1/19*[(1+1/16+1/17+1/18)-(1/16+1/17+1/18)]=1/19