Question

1.3.5+3.5.7+5.7.9+...2013.2015.2017 +2015.2017.2019

giải chi tiết

Answer 1

Ta có:
A=1.3.5+3.5.7+5.7.9+...................+2015.2017.2019

8A=1.3.5.8+3.5.7.8+5.7.9.8+.......................+2015.2017.2019.8

8A=1.3.5.(7+1)+3.5.7.(9-1)+5.7.9.(11-3)+......................+2015.2017+2019.(2021-2013)

8A=1.3.5.7+15+3.5.7.9-1.3.5.7+5.7.9.11-3.5.7.9+.........................+2015.2017.2019.2021-2013.2015.2017.2019

8A=15+2015.2017.2019.2021

A=(15+2015.2017.2019.2021)/8

t i c k cho mình nha mình suy nghĩ khá lâu đấy

 

Answer 2

tôi giải lâu rồi