Question

A=9/1.2+9/2.3+...+9/2020.2021+9/2021.2022

giup minh luon voi 

Answer 1

A = 9/1.2 + 9/2.3 + 9/3.4 + .. + 9/98.99 + 9/99.100
             = 1 - 9/100
             = 100/100 - 9/100
              = 91/100

Answer 2

\(A=9\left(1-\dfrac{1}{2}+\dfrac{1}{2}-\dfrac{1}{3}+...+\dfrac{1}{2021}-\dfrac{1}{2022}\right)\)

\(A=9\left(1-\dfrac{1}{2022}\right)=9.\dfrac{2021}{2022}=\dfrac{18189}{2022}=\dfrac{6063}{674}\)

Answer 3