`1/[1xx3]+1/[3xx5]+1/[5xx7]+...+1/[17xx19]`
`=1/2xx(2/[1xx3]+2/[3xx5]+....+2/[17xx19])`
`=1/2xx(1-1/3+1/3-1/5+....+1/17-1/19)`
`=1/2xx(1-1/19)`
`=1/2xx18/19`
`=9/19`
1/3x5+1/5x7+1/7x9...........1/17x19+1/x(x-2)
a=1/1x3=1/3x5+1/5x7+....+1/2019x2021+1/2021x2023
1/1x3+1/3X5+1/5X7+1/7X9+…+1/99X101
1/1x3 + 1/3x5 + 1/5x7 + 1/7x9 + 1/9x11
A= 1/(1x3) + 1/(3x5)+ 1/(5x7) + 1/(7x9) + 1/(9x11) = ?
Bài 1:Tính
A=1/1x3+1/3x5+1/5x7+.......+1/2009x2011
0,75-(13/11-50%):5/11
A=1/6+1/12+1/20+1/30+1/42+1/56+1/72
B=2/1x3+2/3x5+2/5x7+...+2/49x51
Dấu / là phần nha. Giúp mik với đang cần gấp!!!
4/1x3+4/3x5+4/5x7+...+4/25x27
giúp mình với mình đag cần gấp
chứng minh rằng tổng S=1/1x3+1/3x5+1/5x7+.............+1/2015x2017<1/2
