Question

tính tổng: 2/11x13 + 2/13x15 + 2/15x17 +...+ 2/95x97 + 2/97x99

Answer 1

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

Answer 2

thank you 

Answer 3

= 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

Answer 4

\(\frac{2}{11.13}+\frac{2}{13.15}+\frac{2}{15.17}+..+\frac{2}{95.97}+\frac{2}{97.99}\)

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

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

\(=\frac{98}{99}\)