1/1.2 + 1/2.3 + .... + 1/x.(x+1) = 1/2
1 - 1/2 + 1/2 - 1/3 + ... + 1/x + 1/x+1 = 1/2
1 - 1/x+1 = 1/2
1/x+1 = 1 - 1/2
1/x+1 = 1/2
=> x + 1 = 2
x = 2 - 1
x = 1
Tìm X ( x này là nhân )
\(\frac{1}{1x2}+\frac{1}{2x3}+.....+\frac{1}{Xx\left(x+1\right)}=\frac{9}{10}\)
(1/1x2+1/2x3+1/3x4.....1/7x8+1/8x9)x100-[5/2-(x+206/100)]:1/2=89
1/1x2 + 1/2x3 + ... + 1/Xx(X+1) = 2019/2020
Giúp mk vs chiều nộp r ai nhanh, đúng chỉ tiết mk tk cho 2 -> 3 cái nhoa!!
1/1x2 + 1/2x3 + 1/3x4 + ... 1/99 x 100
(1-1/2)(1-1/3)(1-1/4)….(1-1/2002).x=1-1/1x2-1/2x3-1/3x4-...1/2002x2003
6)chứng tỏ
a)1/1x2+1/2x3+...+1/9x10 <1
b)1/1x2+1/2x3+...+1/99x100 <1
a)4/1x5+1/5x9+1/9x13+1/13x17+1/17x21<1
Lưu ý:"x" là phép nhân
Tìm x biết 1/1x2 + 1/2x3 + 1/3x4 + ... + 1/X(X+1) = 99/100
b, B = 1\(\frac{1}{1x2}+\frac{1}{2x3}+......+\frac{1}{99x100}\)
c, C = \(\frac{1}{1x2}+\frac{1}{2x3}+......+\frac{1}{n\left(n+1\right)}\)
d, D = 1 + 2 + 3 + ......+ n
