Все на картинке
S_(n)=(1/(7*8))+((1/(8*9))+...+(1/(n+6)*(n+7)))= =(1/7)-(1/8)+(1/8)-(1/9)+...+(1/(n+6))-(1/(n+7))= =(1/7)-...(1/(n+7)) S=lim_(n→∞)S_(n)=1/7