Question

Tính

\(\frac{1}{9x11}+\frac{1}{11x13}+\frac{1}{13x15}+.......+\frac{1}{97x99}\)

Answer 1

Mọi người giúp mik với mik đang cần gấp

Answer 2

\(=\frac{1}{2}\times\left(\frac{1}{9}-\frac{1}{11}+\frac{1}{11}-\frac{1}{13}+...+\frac{1}{97}-\frac{1}{99}\right)\)

\(=\frac{1}{2}\times\left(\frac{1}{9}-\frac{1}{99}\right)\)

\(=\frac{1}{2}\times\frac{10}{99}\)

\(=\frac{5}{99}\)

Answer 3

\(\frac{1}{9}-\frac{1}{11}+\frac{1}{11}-\frac{1}{13}+\frac{1}{13}-\frac{1}{15}+....+\frac{1}{97}-\frac{1}{99}=\frac{1}{9}_{ }-\frac{1}{99}=\)\(\frac{10}{99}\)

Answer 4

\(\frac{1}{9\times11}+\frac{1}{11\times13}+....+\frac{1}{97\times99}\)

\(=\frac{1}{9}-\frac{1}{11}+\frac{1}{11}-\frac{1}{13}+....+\frac{1}{97}-\frac{1}{99}\)

\(=\frac{1}{9}-\frac{1}{99}\)

\(=\frac{1}{9}+\frac{-1}{99}=\frac{11}{99}+\frac{-1}{99}\)

\(=\frac{10}{99}\)

Answer 5

\(\frac{1}{2}.\left(\frac{2}{9.11}+\frac{2}{11.13}+\frac{2}{13.15}+...+\frac{2}{97.99}\right)\)

\(=\frac{1}{2}\left(\frac{1}{9}-\frac{1}{11}+\frac{1}{11}-\frac{1}{13}+...+\frac{1}{97}-\frac{1}{99}\right)\)

\(=\frac{1}{2}.\left(\frac{1}{9}-\frac{1}{99}\right)\)

\(=\frac{1}{2}.\frac{10}{99}\)

\(=\frac{5}{99}\)

học tốt

Answer 6

\(A=\frac{1}{9.11}+\frac{1}{11.13}+\frac{1}{13.15}+...+\frac{1}{97.98}\)

\(2A=2\left(\frac{1}{9.11}+\frac{1}{11.13}+\frac{1}{13.15}+...+\frac{1}{97.98}\right)\)

\(2A=\frac{2}{9.11}+\frac{2}{11.13}+\frac{2}{13.15}+...+\frac{1}{97.98}\)

\(2A=1-\frac{1}{9}+\frac{1}{11}-\frac{1}{11}+...+\frac{1}{97}-\frac{1}{98}\)

\(2A=1-\frac{1}{98}\)

\(2A=\frac{97}{98}\)

Answer 7

Huỳnh tấn nam, im lặng, Doraeiga sai rồi nhé