\(\frac{1}{2}+\frac{1}{6}+............+\frac{1}{9900}\)

\(=\frac{1}{1.2}+\frac{1}{2.3}+............+\frac{1}{99.100}\)

\(=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+...........+\frac{1}{99}-\frac{1}{100}\)

\(=1-\frac{1}{100}\)

\(=\frac{99}{100}\)

99

100

A=  2 + 6 + 12 + 20 + ...... + 9702 + 9900

A = 1.2 + 2.3 + 3.4 + ......... + 98 . 99 + 99.100

3A = 1.2.3 + 2.3.3 + 3.4.3 + .... + 99.100.3

3A = 1.2.3 + 2.3.(4-1) + ....+ 99.100.(101-98)

3A = 1.2.3 + 2.3.4 - 1.2.3 + ..... + 99.100.101 - 98.99.100

3A = 99 . 100 . 101

A = 99 . 100 . 101 : 3

A = 333300

A=1.2+2.3+3.4+4.5+....+.....

3A=.....

Bạn biets làm rồi đúng ko

Tích mk nha hùng

T= 1 - 1/2 + 1/2 - 1/3 + ......+ 1/99 - 1/100

  = 1 - 1/100

  = 99/100

\(t=\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{99.100}\)

\(t=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+...+\frac{1}{99}-\frac{1}{100}\)

\(t=1-\frac{1}{100}=\frac{99}{100}\)

Vậy \(t=\frac{99}{100}\)

dấu . hiểu là phép nhân nhé

tớ cũng nghĩ là 99/100

T= 1/1.2+1/2.3+1/3.4+...+1/99.100

T=1-1/2+1/2-1/3+1/3-1/4+...+1/99-1/100

T=1- 1/100

T= 99/100

đúng cho mình nha bạn

Bài này đơn giản mà bạn

Biến đôi T = \(\frac{1}{1.2}+\frac{1}{2.3}+.....+\frac{1}{99.100}\)

\(T=\frac{1}{1}-\frac{1}{2}+\frac{1}{2}-......-\frac{1}{100}\)

\(T=\frac{100}{100}-\frac{1}{100}=\frac{99}{100}\)

T=99/100

ta có : t = 1/1.2 + 1/2.3 + 1/3.4 + .... + 1/98.99 + 1/99.100

=> t = 1/1 - 1/2 + 1/2 - 1/3 + .... + 1/99 - 1/100

=> t = 1 - 1/100

=> t = 99/100

T=1/1x2+1/2x3+1/3x4+....................+1/98x99+1/99x100

T=1-1/2+1/2-1/3+..............+1/98-1/99+1/99-1/100

T=1-1/100

T=99/100

T=1/2+1/6+1/12+..............+1/9702+1/9900

T=1/1x2+1/2x3+1/3x4+...........+1/98x99+1/99x100

T=1-1/2+1/2-1/3+1/3-1/4+.........+1/98-1/99+1/99-1/100

T=1-1/100

T=99/100

           Vậy T=99/100

Giải :

Đặt : A = \(\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+....+\frac{1}{9702}+\frac{1}{9900}\)

\(\Rightarrow A=\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}+....+\frac{1}{98.99}+\frac{1}{99.100}\)

\(\Rightarrow A=\frac{1}{1}-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+...+\frac{1}{98}-\frac{1}{99}+\frac{1}{99}-\frac{1}{100}\)

\(\Rightarrow A=1-\frac{1}{100}=\frac{99}{100}\)

99/100 duyệt đi