Răspuns:
Explicație pas cu pas:
1/1*7+1/7*13+1/13*19+....1/91*97
1/1*7=(1/6)*(1/1-1/7)
1/7*13=(1/6)*(1/7-1/13)
1/13*19=(1/6)(1/13-1/19)
.........................
1/91*97=(1/6)*(1/91-1/97)
toat suma
(1/6) * (1-1/7+1/7-1/13+1/13-1/19+.....+1/91-1/97)=
(1/6)*(1-1/97)
(1/6)*96/97=16/97