`B = 16/(3.5)^2 + 24/(5.7)^2 + 32/(7.9)^2 + ... + 784/(195.197)^2 + 792/(197.199)^2`

Tacó `:`

`B=16/(3.5)^2+24/(5.7)^2+32/(7.9)^2+...+784/(195.197)^2+792/(197.199)^2`

`B=`$\dfrac{5^2-3^2}{3^2.5^2}$`+`$\dfrac{7^2-5^2}{5^2.7^2}$`+`$\dfrac{9^2-7^2}{7^2.9^2}$`+...+`$\dfrac{197^2-195^2}{195^2.197^2}$`+`$\dfrac{199^2-197^2}{197^2.199^2}$

`B=1/3^2-1/5^2+1/5^2-1/7^2+1/7^2-1/9^2+...+1/195^2-1/197^2+1/197^2-1/199^2`

`B=1/3^2-1/199^2`

`B=1/9-1/199^2`

Vì `1/9-1/199^2<1/9`

`->B<1/9(đpcm)  `