2/11x13+2/13x15+2/15x17+...+2/97x99

=1/11-1/13+1/13-1/15+1/15-1/17+...+1/97-1/99

=1/11-1/99

=8/99

thank you 

= 2/11.13 + 2/13.15 + ... + 2/97.99

= 2/11 .2/13 + 2/13 . 2/15 + ... + 2/97 . 2/97

= 2/11 + 2/97

= ......tu tinh

=2/11+2/13-2/13+2/15-2/15+...-2/97+2/98

=2/11+(2/13-2/13+2/15-2/15+...-2/97+2/99)

=2/11+2/99

=20/99

\(\frac{2}{11}\times13+\frac{2}{13}\times15+\frac{2}{15}\times17+........+\frac{2}{97}\times99\)

\(A\times2=\frac{2}{11\times13}+\frac{2}{13\times15}+\frac{2}{15\times17}+........+\frac{2}{97\times99}\)

\(A\times2=\frac{1}{11}-\frac{1}{13}+\frac{1}{13}-\frac{1}{15}+\frac{1}{15}-\frac{1}{17}+........+\frac{1}{97}-\frac{1}{99}\)

\(A=\frac{1}{11}-\frac{1}{99}\)

\(A=\frac{8}{99}\)

mik ko bt là có đúng hay ko nhưng đúng thì các bạn cho 1 t i c k nha

A=\(\frac{4}{11}-\frac{4}{13}+\frac{4}{13}-\frac{4}{15}+...+\frac{4}{99}-\frac{4}{101}\)

\(A=4\left(\frac{1}{11}-\frac{1}{13}+\frac{1}{13}-\frac{1}{15}+...+\frac{1}{99}-\frac{1}{101}\right)\)

\(A=4.\left(\frac{1}{11}-\frac{1}{101}\right)\)

A=4. 90/1111=360/1111

Co dung khong vay Cuong Lucha DT

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6,712565785

\(\frac{2}{11x13}+\frac{2}{13x15}+\frac{2}{15x17}+...+\frac{2}{97x99}\)

\(=\frac{1}{11}-\frac{1}{13}+\frac{1}{13}-\frac{1}{15}+\frac{1}{15}-\frac{1}{17}+...+\frac{1}{97}-\frac{1}{99}\)

\(=\frac{1}{11}-\frac{1}{99}\)

\(=\frac{8}{99}\)

Ta có:

\(\frac{2}{11.13}+\frac{2}{13.15}+\frac{2}{15.17}+...+\frac{2}{97.99}\)

\(=\frac{2}{11}-\frac{2}{13}+\frac{2}{13}-\frac{2}{15}+\frac{2}{15}-\frac{2}{17}+...+\frac{2}{97}-\frac{2}{99}\)

\(=\frac{1}{11}-\frac{1}{13}+\frac{1}{13}-\frac{1}{15}+\frac{1}{15}-\frac{1}{17}+...+\frac{1}{97}-\frac{1}{99}\)

\(=\frac{1}{11}-\frac{1}{99}=\frac{8}{99}\)

Sửa lại đề bài nhé:

\(\frac{2}{11x13}+\frac{2}{13x15}+\frac{2}{15x17}+.........+\frac{2}{97x99}\)

= \(\frac{2}{11}-\frac{2}{13}+\frac{2}{13}-\frac{2}{15}+\frac{2}{15}-\frac{2}{17}+..........+\frac{2}{97}-\frac{2}{99}\)

Sau khi trực tiêu hết ta có:

= \(\frac{2}{11}-\frac{2}{99}\)

= \(\frac{16}{19}\)

8/99 nha bạn

(1/11-1/13+1/13-1/15+.....+1/19-1/21)*462-y=19

(1/11-1/21)*462-y=19

10/231*462-y=19

20-y=19

y=1

\(\left(\frac{2}{11x13}+\frac{2}{13x15}+\frac{2}{15x17}+\frac{2}{17x19}+\frac{2}{19x21}\right)\)) x 462 - y = 19

\(=\left(\frac{13-11}{11x13}+\frac{15-13}{13x15}+\frac{17-15}{15x17}+\frac{19-17}{17x19}+\frac{21-19}{19x21}\right)\)x 462 - y = 19

\(=\frac{1}{11}-\frac{1}{13}+\frac{1}{13}-\frac{1}{15}+\frac{1}{15}-\frac{1}{17}+\frac{1}{17}-\frac{1}{19}+\frac{1}{19}-\frac{1}{21}\)) x 462 - y = 19

\(=\left(\frac{1}{11}-\frac{1}{21}\right)\)x 462 - y = 19

\(=\left(\frac{21}{231}-\frac{11}{231}\right)\)x 462 - y = 19

\(=\frac{10}{231}\)x 462 - y = 19

\(=20\)- y = 19

                y = 20 - 19

                y = 1

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