`A=4/[5.7]+4/[7.9]+4/[9.11]+...+4/[21.23]+4/[23.25]`
`A=2.(2/[5.7]+2/[7.9]+....+2/[23.25])`
`A=2.(1/5-1/7+1/7-1/9+....+1/23-1/25)`
`A=2.(1/5-1/25)`
`A=2. 4/25`
`A=8/25`
B=1/3.5+1/5.7+1/7.9+....+1/21.23+1/23.25
4/5.7+4/7.9+4/9.11+...+4/53.55 = ?
Tính tổng 4/1.3+4/3.5+4/5.7+4/7.9+4/9.11+.....+4/2013.2015
\(\left(\frac{4}{5.7}+\frac{4}{7.9}+\frac{4}{9.11}+...+\frac{4}{53.55}\right)\)
giúp mình bài này nha,nhanh lên đó,mai là hạn cuối rồi
Đề bài:
4/3.5+4/5.7+4/7.9+4/9.11
tinh nhanh:s=2/5.7+2/7.9+2/9.11+...+2/93.95+3/95.98+4/98.102+5/102.107+2012/107.2119
Tính nhanh tổng sau:
A=1/3+1/6+1/10+1/15+1/21+1/28
B=1/5.7+1/7.9+1/9.11+....+1/23.25
a,2/5.7 + 2/7.9 + 2/9.11 + ... + 2/53.55
b,1/2 .1/3 +1/4 . 1/5 + ... + 1/8 . 1/9
c,(1+1/2)(1+1/3)(1=1/4).....(1+1/99)
Tìm x, biết:
x/3.5 + x/5.7 + x/7.9 + x/9.11 + x/11.13 + x/13.15 = 4/45
