Toán tính tổng A=3mũ 2020 -3 mũ 2019+3 mũ 2018- 3 mũ 2017+…….+3 mũ2 -3 +1 16/11/2021 By Clara tính tổng A=3mũ 2020 -3 mũ 2019+3 mũ 2018- 3 mũ 2017+…….+3 mũ2 -3 +1
Tham khảo `A=3^{2020}-3^{2019}+3^{2018}-3^{2017}+…+3^2-3+1` `⇒3A=3^{2021}-3^{2020}+3^{2019}-3^{2018}+…+3^3-3^2+3` `⇒3A+A=3^{2021}-3^{2020}+3^{2019}-3^{2018}+…+3^3-3^2+3-(3^{2020}-3^{2019}+3^{2018}-3^{2017}+…+3^2-3+1)` `⇒4A=3^{2021}+1` `⇒A=\frac{3^{2021}+1}{4}` Trả lời
`A=3^2020 -3^2019+3^2018- 3^2017+…….+3^2 -3 +1` `3A = 3^2021 -3^2020+3^2019- 3^2018+…….+3^3 -3^2 +3` `3A+A=( 3^2021 -3^2020+3^2019- 3^2018+…….+3^3 -3^2 +3)`+`(3^2020 -3^2019+3^2018- 3^2017+…….+3^2 -3 +1)` `4A = 3^2021 + 1` `A = (3^2021 + 1)/4` XIN HAY NHẤT Ạ Trả lời
Tham khảo
`A=3^{2020}-3^{2019}+3^{2018}-3^{2017}+…+3^2-3+1`
`⇒3A=3^{2021}-3^{2020}+3^{2019}-3^{2018}+…+3^3-3^2+3`
`⇒3A+A=3^{2021}-3^{2020}+3^{2019}-3^{2018}+…+3^3-3^2+3-(3^{2020}-3^{2019}+3^{2018}-3^{2017}+…+3^2-3+1)`
`⇒4A=3^{2021}+1`
`⇒A=\frac{3^{2021}+1}{4}`
`A=3^2020 -3^2019+3^2018- 3^2017+…….+3^2 -3 +1`
`3A = 3^2021 -3^2020+3^2019- 3^2018+…….+3^3 -3^2 +3`
`3A+A=( 3^2021 -3^2020+3^2019- 3^2018+…….+3^3 -3^2 +3)`+`(3^2020 -3^2019+3^2018- 3^2017+…….+3^2 -3 +1)`
`4A = 3^2021 + 1`
`A = (3^2021 + 1)/4`
XIN HAY NHẤT Ạ