Toán Lớp 6: a) Tính nhanh
2021.1001-2021
b) cho :
S = 1+ 5^2+ 5^4+ 5^6+……+5^2020
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Toán Lớp 6: a) Tính nhanh
2021.1001-2021
b) cho :
S = 1+ 5^2+ 5^4+ 5^6+……+5^2020
Comments ( 2 )
=2021.1000
=2021000
b) Cho: S = 1+ 5^2+ 5^4+ 5^6+……+5^2020
=>S.5=5.(1+ 5^2+ 5^4+ 5^6+……+5^2020)
=>S.5=5^1+ 5^2+ 5^4+ 5^6+……+5^2020+5^2021
=>S.5-S=(5^1+ 5^2+ 5^4+ 5^6+……+5^2020+5^2021)-(1+ 5^2+ 5^4+ 5^6+……+5^2020)
=>S.5-S=5^2021-1
=>S.4=5^2021-1
=>S=5^2021-1:4
~Học tốt nhen
Nhớ tick nhé<3