A= 1/10+1/11+1/12+1/13+...........+1/99+1/100
2A=1/9+1/10+1/11+1/12+...........+1/98+1/99
2A-A=(1/10+1/11+1/12+1/13+.............+1/99+1/100)-(1/9+1/10+1/11+1/12+............1/98+1/99)
A=1/100-1/9
$\frac{1}{10^2}+\frac{1}{11^2}+\frac{1}{12^2}+...+\frac{1}{100^2}<\frac{3}{4}$
Làm hộ mình cái mấy thánh!!!!!!!