Răspuns:
Explicație pas cu pas:
S = 1+1/5+1/5^2+...+1/5^14
S/5 = 1/5+1/5^2+...+1/5^14 + 1/5^15
S - S/5 = 4S/5 = 1 + 1/5 + 1/5^2 +...+ 1/5^14 - 1/5 - 1/5^2 -....- 1/5^14 - 1/5^15
4S/5 = 1 - 1/5^15
4S = 5 - 1/5^14
S = 5/4 - 1/4*5^15