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17 tháng 5 2021

   2020 × 2021 - 1000 - 2020 × 2019 - 1020

= 2020 × 2021 - 2020 × 2019 - 1000 - 1020

= 2020 × 2021 - 2020 × 2019 - (1000 + 1020)

= 2020 × 2021 - 2020 × 2019 - 2020

= 2020 × 2021 - 2020 × 2019 - 2020 × 1

= 2020 × (2021 - 2019 - 1)

= 2020 × 1

= 2020.

26 tháng 2 2020

1)1-2+3-4+5-6+...+1019-1020 (có 1020 số hạng)

= (1-2+3-4) + (5-6+7-8) +.....+(1017-1018+1019-1020) (có 225 nhóm)

= -2 +(-2) +...........+(-2) ( có 225 số hạng)

= -2.225

= -450

5)1+2-3-4+...+97+98-99-100

= (1+2-3-4) +..........+(97+98-99-100)

= (-4) +..........(-4)

= (-4). 25

= -100

26 tháng 2 2020

2)(-1)+2+(-3)+4+...+(-99)+100

= -1 +2 -3+4+.....-99+100

= (2-1) +(4-3) +....+(100-99) ( Có 50 cặp )

= 1+ 1+...+1 ( Có 50 số )

=1.50

=50

4) Nếu đổi +48 thành -48 thì mik làm đc

2-4+6-8+...-48-50

= 2+ (6-4) + (10-8) + ...+(50-48)

=2+2+2+....+2

=2.13

=26

17 tháng 8 2016

\(1020+Xx\frac{1}{3}=\frac{4}{5}+1020\)

\(=1020+Xx\frac{1}{3}=\frac{5104}{5}\)

\(=Xx\frac{1}{3}=\frac{5104}{5}-1020\)

\(=Xx\frac{1}{3}=\frac{4}{5}\)

\(=\frac{4}{5}:\frac{1}{3}\)

\(=\frac{12}{5}\)

17 tháng 8 2016

\(1020+x.\frac{1}{3}=\frac{4}{5}+1020\)

\(1020+x.\frac{1}{3}=\frac{5104}{5}\)

\(x.\frac{1}{3}=\frac{5104}{5}-1020\)

\(x.\frac{1}{3}=\frac{4}{5}\)

\(x=\frac{4}{5}:\frac{1}{3}\)

\(x=\frac{12}{5}\)

♥ ☼ ↕ ✿ ⊰ ⊱ ✪ ✣ ✤ ✥ ✦ ✧ ✩ ✫ ✬ ✭ ✯ ✰ ✱ ✲ ✳ ❃ ❂ ❁ ❀ ✿ ✶ ✴ ❄ ❉ ❋ ❖ ⊹⊱✿ ✿⊰⊹ ♧ ✿ 

\(A=\frac{2019^{2020}+1}{2019^{2021}+1}\)và \(B=\frac{2019^{2018}+1}{2019^{2019}+1}\)

Xét \(A=\frac{2019^{2020}+1}{2019^{2021}+1}\Rightarrow2019A=\frac{2019^{2021}+2019}{2019^{2021}+1}=1+\frac{2019}{2019^{2021}+1}\)

Xét \(B=\frac{2019^{2018}+1}{2019^{2019}+1}\Rightarrow2019B=\frac{2019^{2019}+2019}{2019^{2019}+1}=1+\frac{2018}{2019^{2019}+1}\)

Vì \(1+\frac{2018}{2019^{2021}+1}< 1+\frac{2018}{2019^{2019}+1}\Rightarrow\frac{2019^{2020}+1}{2019^{2021}+1}< \frac{2018^{2019}+1}{2019^{2019}+1}\)

\(\Rightarrow A< B\)

Ta có:

\(A=\frac{2019^{2020}+1}{2019^{2021}+1}\)

\(\Rightarrow2019A=\frac{2019^{2021}+2019}{2019^{2021}+1}\)

\(\Rightarrow2019A=1+\frac{2019}{2019^{2021}+1}\)

\(\Rightarrow A=1+\frac{2019}{2019^{2021}+1}:2019\)

Ta lại có:

\(B=\frac{2019^{2018}+1}{2019^{2019}+1}\)

\(\Rightarrow2019B=\frac{2019^{2019}+2019}{2019^{2019}+1}\)

\(\Rightarrow2019B=1+\frac{2019}{2019^{2019}+1}\)

\(\Rightarrow B=1+\frac{2019}{2019^{2019}+1}:2019\)

Do \(2019^{2021}+1>2019^{2019}+1\)

\(\Rightarrow\frac{2019}{2019^{2021}+1}< \frac{2019}{2019^{2019}+1}\)

\(\Rightarrow1+\frac{2019}{2019^{2021}+1}:2019< 1+\frac{2019}{2019^{2019}+1}:2019\)

\(\Rightarrow A< B\)

Vậy \(A< B.\)