Question

1/15+1/35+1/63+...+1/9999

 

Answer 1

Đặt A=1/15+1/35+...+1/9999

=> A=1/(3*5)+1/(5*7)+...+1/(99*101)

=> A=1/3-1/5+1/5-1/7+...+1/99-1/101

=> A=1/3-1/101

=> A=101/303-3/303

=> A=98/303