Tính : `1/(1.2) + 1/(2.3) + … + 1/(49.50)`

$\dfrac1 {1.2} + \dfrac1 {2.3} + … + \dfrac1 {49.50}$

$\dfrac{2-1} {1.2} + \dfrac{3-2} {2.3} + … + \dfrac{50-49} {49.50}$

$=\dfrac1 {1}-\dfrac1 {2} + \dfrac1 {2} -\dfrac1 {3}+ … + \dfrac1 {49}-\dfrac1 {50}$

$=\dfrac1 {1}-\dfrac1 {50}$

$=\dfrac{49} {50}$