thiếu đề rồi

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

\(S=2000.\left(\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+...+\frac{1}{9900}\right)=2000.\left(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+....+\frac{1}{99.100}\right)\)

  \(=2000.\left(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+....+\frac{1}{99}-\frac{1}{100}\right)=2000.\left(1-\frac{1}{100}\right)=20.99=1980\)

D=\(1-\frac{1}{2}+1-\frac{1}{6}+1-\frac{1}{12}+........+1-\frac{1}{9900}\)

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

\(=99-\left(\frac{1}{1.2}+\frac{1}{2.3}+....+\frac{1}{99.100}\right)\)

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

\(=99-\left(1-\frac{1}{100}\right)=98+\frac{1}{100}=\frac{9801}{100}\)

d=1/1.2+5/2.3+11/3.4+...+9899/99.100

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

=>d=1-1/100

=>d=99/100

Vậy d=99/100

99/100

\(A=1+\frac{2}{6}+\frac{2}{12}+...+\frac{2}{9702}+\frac{2}{9900}=1+\frac{2}{2.3}+\frac{2}{3.4}+...+\frac{2}{98.99}+\frac{2}{99.100}\)

=> \(A=1+2\left(\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{98.99}+\frac{1}{99.100}\right)\)

\(A=1+2\left(\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{98}-\frac{1}{99}+\frac{1}{99}-\frac{1}{100}\right)\)

\(A=1+2\left(\frac{1}{2}-\frac{1}{100}\right)=1+2.\frac{49}{100}=1+\frac{49}{50}=\frac{99}{50}\)

Đáp số: \(A=\frac{99}{50}\)

thanks bạn nha Bùi Thế Hào 

A=2/2+2/6+2/12+...+2/9900

A=2(1/1.2+1/2.3+1/3.4+...+1/99.100)

A=2(1-1/2+1/2-1/3+1/3-1/4+.....+1/99-1/100)

A=2(1-1/100)

A=2.99/100

A=99/55

Vậy A=99/55

\(\left(1-\frac{2}{6}\right)\left(1-\frac{2}{12}\right)...\left(1-\frac{2}{9900}\right)\)

\(=\frac{4}{6}.\frac{10}{12}...\frac{9898}{9900}\)

\(=\frac{1.4}{2.3}.\frac{2.5}{3.4}...\frac{98.101}{99.100}\)

\(=\frac{1.2...98}{3.4...100}.\frac{4.5...101}{2.3...99}\)

\(=\frac{2}{99.100}.\frac{100.101}{2.3}\)

\(=\frac{101}{99.3}\)

\(=\frac{101}{297}\)

đáp số:\(\frac{101}{297}\)

ai k mk mk sẽ k lại ^-^

là 101/247

l

nhanh nha mình đang cần

    1/2 + 1/6 + 1/12 + ... + 1/9900 + 1/10100

= 1/1.2 + 1/2.3 + 1/3.4 +... +1/99.100 + 1/100.101

= 1/1 - 1/2 + 1/2 + 1/3 - 1/3 + 1/4 +... + 1/99 - 1 / 100 + 1/100 - 1/101

= 1/1 - 1/101

= 100 /101

\(\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+.....+\frac{1}{9900}+\frac{1}{10100}\)

=\(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+.......+\frac{1}{99.100}+\frac{1}{100.101}\)

=\(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+.....+\frac{1}{99}-\frac{1}{100}+\frac{1}{100}-\frac{1}{101}\)

=\(1-\frac{1}{101}\)

=\(\frac{100}{101}\)

Mik trả lời ở bài dưới rồi đó.

o dau ha ho thu giang