\(3xC=\frac{3}{1x2x3x4}+\frac{3}{2x3x4x5}+...+\frac{3}{97x98x99x100}\)
\(3xC=\frac{4-1}{1x2x3x4}+\frac{5-2}{2x3x4x5}+...+\frac{100-97}{97x98x99x100}\)
\(3xC=\frac{1}{1x2x3}-\frac{1}{2x3x4}+\frac{1}{2x3x4}+\frac{1}{3x4x5}+...+\frac{1}{97x98x99}-\frac{1}{98x99x100}\)
\(3xC=\frac{1}{1x2x3}-\frac{1}{98x99x100}\Rightarrow C=\frac{\frac{1}{6}-\frac{1}{98x99x100}}{3}\)
cách tính bài : B = 1/1x2x3x4 + 1/2x3x4x5+ ... + 1/27x28x29x30
A = 1x2x3x4 - 2x3x4x5 + 3x4x5x6 - 4x5x6x7 +...+ 2525x2526x2527x2528?
Tính A = 1x2x3x4 - 2x3x4x5 + 3x4x5x6 - 4x5x6x7 +...+ 2525x2526x2527x2528
C=1x2+2x3+3x4+........+99x100
D=1x2x3+2x3x4+3x4x5+.......+98x99x100
E=12+22+52+.......+992
F=1/1x2+1/2x3+..........+1/99x100
G=1/1x2x3+1/2x3x4+........+1/99x98x100
H= 1/1x2x3x4+1/3x4x5x6+............+1/97x98x99x100
K= 1+1/2(1+2)+1/3(1+2+3)+........+1/30(1+2+30)
L=1/21+1/22+1/23+1/24+..............+1/210
M=2015/2015x2017-20162
\(\frac{ }{ }\)
CT: 1/1x2+ 1/1x2x3+ 1/1x2x3x4+ ..................+ 1/1x2x3x4x5.........100
CMR:
1/1x2 + 1/1x2x3 + 1/1x2x3x4 + ... + 1/1x2x3x...x100 <1
1x2+1x2x3+1x2x3x4+1x2x3x4x5+....+1x2x3...99x100
1x2x3x4x....x9 - 1x2x3x4x...x.8 - 1x2x3x4....x8^2
1x2x3x4:5:6:7:8x9....x1998x1999x2000
Please!Help me :'3
