Question

tính tổng sau:S=2²+3²+4²+.....+2019²

Answer 1

S=4078378

Cách làm;

S=2^2+3^2=4^2+......+2019^2

S=(2+3+4+.....+2019)^2

Số số hạng(trong ngoặc nhé)là

(2019-2):1+1=2018

S=(2019+2).2018=4078378

=>S=4078378

Answer 2

A=22+23+24+...+22019A=1+22+23+24+...+22019

⇔2A=23+24+25+...+22020⇔2A=2+23+24+25+...+22019

⇔2A - A = \(2^{2020}-2^{^2}\)

\(\Leftrightarrow A=2^{^2}\left(2^{^{2019}}-1\right)\)

Answer 3

ông anh làm cái j vậy

Answer 4

S=2²+3²+4²+...+2019²

S=2.2+3.3+4.4+...+2019.2019

S=2.(3-1)+3.(4-1)+4.(5-1)+....+2019.(2020-1)

S=2.3-2.1+3.4-3.1+4.5-4.1+....+2019.2020-2019.1

S=(2.3+3.4+4.5+.....+2019.2020)-(2+3+4+....+2019)

S⁽¹⁾=(2.3+3.4+4.5+.....+2019.2020)

3S⁽¹⁾=3.(2.3+3.4+4.5+.....+2019.2020)

3S⁽¹⁾=2.3.3+3.4.3+4.5.3+....+2019.2020.3

3S⁽¹⁾=2.3.(4-2)+3.4.(5-2)+4.5.(6-3)+....+2019.2020.(2021-2018)

3S⁽¹⁾=2.3.2+2.3.4-2.3.4+3.4.5-3.4.5+4.5.6-.....-2018.2019.2020+2019.2020.2021

3S⁽¹⁾=2.3.2+2019.2020.2021

S⁽¹⁾=\(\frac{2.3.2+2019.2020.2021}{3}\)

S⁽¹⁾=2747468664

S⁽²⁾=2+3+4+......+2019

           Có 2018 số hạng

S⁽²⁾=(2+2019)x2018:2=2039189

S⁽¹⁾-S⁽²⁾=2747468664-2039189

S           =272729475

Chúc bn học tốt

Answer 5

ông anh chất vồn