Tính tổng : `D = 1 + 5 + 5^{2} + 5^{3} + … + 5^{2014} + 5^{2015}` 12/11/2021 Bởi Melanie Tính tổng : `D = 1 + 5 + 5^{2} + 5^{3} + … + 5^{2014} + 5^{2015}`
`D=1+5+5^{2}+5^{3}+…+5^{2015}` `⇒5D=5+5^{2}+5^{3}+…+5^{2016}` $⇒5D-D=(5+5^{2}+5^{3}+…+5^{2016})-(1+5+5^{2}+5^{3}+…+5^{2015})$ `⇒4D=5^{2016}-1` `⇒D=\frac{5^{2016}-1}{4}` $\text{Xin hay nhất nha!}$ Bình luận
D =1 + 5 + 5^2 + 5^3 + … + 5^2014 + 5^2015 D . 5 = ( 1 + 5 + 5^2 + … +5^2014 +5^2015 ) . 5 = 5 + 5^2 + 5^3 + … + 5^2015 + 5^2016 D .5 – D = ( 5 + 5^2 + 5^3 +… + 5^2015 + 5^2016 ) – ( 1 + 5 + 5^2 + … + 5^2014 + 5^2015 ) D . 4 = 5^2016 – 1 D = ( 5^2016 – 1 ) : 4 CHO MIK XIN CTLHN Ạ Bình luận
`D=1+5+5^{2}+5^{3}+…+5^{2015}`
`⇒5D=5+5^{2}+5^{3}+…+5^{2016}`
$⇒5D-D=(5+5^{2}+5^{3}+…+5^{2016})-(1+5+5^{2}+5^{3}+…+5^{2015})$
`⇒4D=5^{2016}-1`
`⇒D=\frac{5^{2016}-1}{4}`
$\text{Xin hay nhất nha!}$
D =1 + 5 + 5^2 + 5^3 + … + 5^2014 + 5^2015
D . 5 = ( 1 + 5 + 5^2 + … +5^2014 +5^2015 ) . 5
= 5 + 5^2 + 5^3 + … + 5^2015 + 5^2016
D .5 – D = ( 5 + 5^2 + 5^3 +… + 5^2015 + 5^2016 ) – ( 1 + 5 + 5^2 + … + 5^2014 + 5^2015 )
D . 4 = 5^2016 – 1
D = ( 5^2016 – 1 ) : 4
CHO MIK XIN CTLHN Ạ