Question

So sánh ( không tính giá trị cụ thể )

 A= 2019.2019                         B= 2018.2020

 5 tk

Answer 1

Ta có:

B= 2018.2020=2018.( 2019+1)=2018.2019+2018

A= 2019.2019=2019.(2018+1)=2018.2019+2019

Vì 2018.2019+2018<2018.2019+2019

=> 2018.2020<2019.2019
hay B<A

Answer 2

\(A=2019.2019=2019^2\)

\(B=2018.2020=\left(2019-1\right)\left(2019+1\right)=2019^2-1\)

Vì \(2019^2>2019^2-1\)

\(\Rightarrow A>B\)

Answer 3

\(A=2019\cdot2019\)

\(\Rightarrow A=\left(2018+1\right)\cdot\left(2020-1\right)\)

\(\Rightarrow A=\left(2018+1\right)\cdot2020-(2018+1)\cdot1\)

\(\Rightarrow A=2018\cdot2020+2020-2018-1\)

\(\Rightarrow A=2018\cdot2020+1\)

\(\Rightarrow A=B+1\)

\(\Rightarrow A\)>\(B\)

Answer 4

\(B=2018.2020=\left(2019-1\right)\left(2019+1\right)\)

Áp dụng hằng đẳng thức \(A^2-B^2=\left(A+B\right)\left(A-B\right)\)

\(\Rightarrow B=2019^2-1^2=2019.2019-1\)

Vậy A > B