giúp em với ạ, em đg cần gấp '^'

A = $\dfrac{55}{11×16}$ `+` $\dfrac{55}{16×21}$ `+` $\dfrac{55}{21×26}$ `+` $\dfrac{55}{26×31}$ `+` $\dfrac{55}{31×36}$ `+` $\dfrac{55}{36×41}$

`= 11×(` $\dfrac{5}{11×16}$ `+` $\dfrac{5}{16×21}$ `+` $\dfrac{5}{21×26}$ `+` $\dfrac{5}{26×31}$ `+` $\dfrac{5}{31×36}$ `+` $\dfrac{5}{36×41}$ `)`

`= 11×(1/11 - 1/16 + 1/16 - 1/21 + 1/21 - 1/26 + 1/26 - 1/31 + 1/31 - 1/36 + 1/36 - 1/41)`

`= 11×[1/11+(-1/16+1/16)+(-1/21+1/21)+(-1/26+1/26)+(-1/31+1/31)+(-1/36+1/36)-1/41]`

`= 11×(1/11-1/41)`

`= 11×30/451 = 30/41`