3/4+1/1.2+1/2.3+1/3.4+........+1/99.100
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![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(\frac{1.2-1}{2!}+\frac{2.3-1}{3!}+............+\frac{99.100-1}{100!}\)
\(=\frac{1.2}{2!}-\frac{1}{2!}+\frac{2.3}{3!}-\frac{1}{3!}+..........+\frac{99.100}{100!}-\frac{1}{100!}\)
\(=\left(\frac{1.2}{2!}+\frac{2.3}{3!}+.........+\frac{99.100}{100!}\right)-\left(\frac{1}{2!}+\frac{1}{3!}+.....+\frac{1}{100!}\right)\)
\(=\left(1+1+\frac{1}{2!}+.........+\frac{1}{98!}\right)-\left(\frac{1}{2!}+\frac{1}{3!}+....+\frac{1}{100!}\right)\)
\(=2-\frac{1}{99!}-\frac{1}{100!}< 2\)
\(\Rightarrowđpcm\)
![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
ta có 1+(1+2)+(1+2+3)+...+(1+2+3+...+100)
=4+(1+3).3/2+9+(1+4).4/2+...+(1+100).100/2
=1/2(1.2+2.3+.....+100.101)
=>1/2.100.101.102
con cái dưới thì bằng 99.100.101
=>F=51/99
ngu rua mà ko biet lam
![](https://rs.olm.vn/images/avt/0.png?1311)
\(=1-\dfrac{1}{2}+\dfrac{1}{2}-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{4}+...+\dfrac{1}{99}-\dfrac{1}{100}\\ =1-\dfrac{1}{100}=\dfrac{99}{100}\)
=1/1-1/2+1/2-1/3+1/3-1/4+....+1/99-1/100
=1-1/100
=99/100
![](https://rs.olm.vn/images/avt/0.png?1311)
1/1.2 + 1/2.3 + 1/3.4 + ... + 1/99.100
= 1 - 1/2 + 1/2 - 1/3 + 1/3 - 1/4 + ... + 1/99 - 1/100
= 1 - 1/100
= 99/100
Máy mình đang lỗi nên không gõ được công thức, xin lỗi bạn nhé! :'(
SDFGHJKL;'
\(\frac{3}{4}+\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+.........+\frac{1}{99.100}\)
\(=\frac{3}{4}+1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+......+\frac{1}{99}-\frac{1}{100}\)
\(=\frac{3}{4}+1-\frac{1}{100}=\frac{87}{50}\)