    2019 2020 1AB A BTA CÓ

2 . 2 2019.2020

b  a  b a 

       

Nên 2019 2019 a 2020 b 2020 2019 2 2019.2020 2020  2019 2020 

2

b a

Suy ra a b  2019 2020

2

.