Question

so sanh

2019 x 2021 va 2020 x 2020

Answer 1

Ta có:

2019.2021=2019.(2020+1)=2019.2020+2019 (1)

Lại có:

2020.2020=(2019+1).2020=2019.2020+2020 (2)

Vì 2019.2020=2019.2020 mà 2019<2020

=>(1)<(2)

=>..... 

Answer 2

                                                                          Bài giải

Ta có : \(2019\text{ x }2021=2019\text{ x }2020+2019\)

          \(2020\text{ x }2020=2019\text{ x }2020+2020\)

\(\text{Vì }2019\text{ x }2020+2019< 2019\text{ x }2020+2020\text{ }\Rightarrow\text{ }2019\text{ x }2021< 2020\text{ x }2020\)

Answer 3

                                    Bài giải

Ta có : 

\(2019\text{ x }2021=2019\text{ x }2020+2019\)

 \(2020\text{ x }2020=2019\text{ x }2020+2020\)

\(\text{Vì }2019\text{ x }2020+2019< 2019\text{ x }2020+2020\text{ }\Rightarrow\text{ }2019\text{ x }2021< 2020\text{ x }2020\)

Answer 4

2019x2021 = (2020 - 1)x(2020 + 1)  = 2020^2 - 1 < 2020x2020