CT: 1/1x2+ 1/1x2x3+ 1/1x2x3x4+ ..................+ 1/1x2x3x4x5.........100
CMR:
1/1x2 + 1/1x2x3 + 1/1x2x3x4 + ... + 1/1x2x3x...x100 <1
3x - (1/1x2+1/2x3+.....+1/99x100)=1/1x2x3+1/2x3x4+......+1/18x19x20
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
\(\frac{ }{ }\)
tinh
a)A=1x2+2x3+3x4+............+99x100
b)B=1x3+3x5+5x7+............97x99
c)C=1x2x3+2x3x4+..............98x99x100
S1 = __3__+__3__+...+__3__
1x2 2x3 99x100
S2=1+_1_ +_1_+_1_+...+_1_+_1_
2 4 8 2048 4096
S3=__1__+__1__+...+__1__
11x13 13x15 97x99
S4=1x2x3+2x3x4+3x4x5+...+20x21x22
S5__1__+__1__+__1__+...__1__
1x2x3 2x3x4 3x4x5 19x20x21
LÀM ƠN GHI GIÚP MÌNH CÁCH GIẢI NHÉ
Tính H=\(\frac{1}{1x2}\) -\(\frac{1}{1x2x3}\) +\(\frac{1}{2x3}\) -\(\frac{1}{2x3x4}\) +\(\frac{1}{3x4}\) -\(\frac{1}{3x4x5}\) +...+\(\frac{1}{99x100}\) -\(\frac{1}{99x100x101}\)
Tìm số tự nhiên n để số A= 1+1x2+1x2x3+...+1x2x3x...xn là số chính phương (n thuộc N*)
