`c = 4/(3 . 5) + 4/(5. 7) + ... + 4/(97. 99)`
`= 2 . (1/3 - 1/5 + 1/5 - 1/7 + ... + 1/97 - 1/99)`
`= 2 . (1/3 - 1/99)`
`= 2 . (33/99 - 1/99)`
`= 2 . 32/99`
`= 64/99`
`d = 18/(2 . 5) + 18/(5 . 8) +... + 18/(203 . 206)`
`= 6 . (1/2 - 1/5 + 1/5 - 1/8 +... + 1/203 - 1/206)`
`= 6 . (1/2 - 1/206)`
`= 6 . 102/206`
`=612/206`
`= 336/103`
`-> c/d = (64/99)/(336/103) = 412/2079`
Tính
a)\(\frac{4}{3.5}+\frac{4}{5.7}+...+\frac{4}{97.99}\)
b)\(\frac{18}{2.5}+\frac{18}{5.8}+...+\frac{18}{203.206}\)
A= 18/2.5+18/5.8+...+18/203.206 =?
A=1/1.2+1/2.3+1/3.4+1/4.5+...+1/98.99+1/99.100
B=2/1.3+2/3.5+2/5.7+2/7.9+...+2/97.99+2/99.101
C=1/2+1/4+1/8+1/16+...+1/1024+1/2048
D=1/2+1/6+1/18+1/54+1/4374+1/13122 ( . (DẤU CHẤM LÀ ''NHÂN'')
Tính các tổng sau
1 :D = 1.3 +2.3+3.4+........+99.100
2 . E= 1.3 +3.5+5.7+.........+97.99
3.F= 2.4 + 4.6+ 6+8+..........+98.1009
4. G=1.4+2.5+3.6+........+97.100
Giúp mình nhé . Mình cần gấp
Tính nhanh
18/2.5 + 18/5.8 + ...... + 18/103.306
B=18/2.5+18/5.8+..........+18/200.203+18/203.205
Tính nhanh
Dấu chấm là nhân nhé !
Tính tổng:
A= 1/2+1/4+1/8+1/16
B= 75/100+18/21+19/32+1/4+3/21+13/32
C= 2/3.5+2/5.7+2/7.9+...+2/41.43
D= 1/10+1/15+1/21+...+1/120
Thanks
4/1.3 + 4/3.5 + 4/5.7 +...+ 4/ 97.99
\(\frac{4}{3.5}+\frac{4}{5.7}+....+\frac{4}{97.99}\)
tính tổng
4/3.5 + 4/5.7 + 4/7.9 + ... + 4 /97.99 = ?
