A = 2/9 *11 + 2/11*13 + 2/13*15 + ….. + 2/97 * 99. B = 6/5*7 + 6/ 7*9 + … + 6/95+97 + 6/97+99 giup minh nha minh dang can gap lam ai do giup minh

`A=2/(9×11) + 2/(11×13) + 2/(13×15) +…+ 2/(97×99)`

`⇒ A = 1/9 – 1/11 + 1/11 – 1/13 + 1/13 – 1/15 +…+ 1/97 – 1/99`

`⇒ A = 1/9 – 1/99`

`⇒ A = 11/99 – 1/99 = 10/99`

`B=6/(5×7) + 6/(7×9) +…+ 6/(95×97) + 6/(97×99)`

`⇒ B = 3 × (2/(5×7) + 2/(7×9) +…+ 2/(95×97) + 2/(97×99))`

`⇒ B = 3 × (1/5 – 1/7 + 1/7 – 1/9 +…+ 1/95 – 1/97 + 1/97 – 1/99)`

`⇒ B = 3 × (1/5 – 1/99)`

`⇒ B = 3/5 – 1/33`

`⇒ B = 99/165 – 5/165 = 94/165`