=`123456789009895436891619370390615895`96312836092419643527671493963894583594783285675 NHA BẠN!?~~~~~~

Mình nghĩ câu A phải là 11/23.34 mới đúng.

Theo đề mới: A)

11/12 = 11/1.12

Vậy A = 11/1.12 + 11/12.23 + ... + 11/89.100

= 1 - 1/12 + 1/12 - 1/23 + .... + 1/89 - 1/100

= 99/1000

Vậy x là: 2/3 - 99/100 = -97/300

B) 2/11.13 + ... + 2/19.21 = 1/11 - 1/13 + .... + 1/19 - 1/21 = 10/231

=> 10/231 - x = 4/3 - 221/223 = 229/669

=> x = 10/231 - 229/669

=> x = 6690/154539 - 52899/154539

=> x = -46209/154539 = -15403/51513

Giúp mik luôn bài chứng minh đi bạn T.T

Đề sai nhé bạn!

Đề sai chỗ \(\dfrac{11}{12.23}\) nha mấy bạn mk nghi nhầm

đề sai sao làm bạn nên sửa cho bọn tui nha

a.

\(\left(\frac{11}{12}+\frac{11}{12\times23}+\frac{11}{23\times34}+...+\frac{11}{89\times100}\right)+x=\frac{2}{3}\)

\(\left(\frac{11}{12}+\frac{1}{12}-\frac{1}{23}+\frac{1}{23}-\frac{1}{34}+...+\frac{1}{89}-\frac{1}{100}\right)+x=\frac{2}{3}\)

\(\left(\frac{11}{12}+\frac{1}{12}-\frac{1}{100}\right)+x=\frac{2}{3}\)

\(\left(\frac{12}{12}-\frac{1}{100}\right)+x=\frac{2}{3}\)

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

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

\(\frac{99}{100}+x=\frac{2}{3}\)

\(x=\frac{2}{3}-\frac{99}{100}\)

\(x=\frac{200-297}{300}\)

\(x=-\frac{97}{300}\)

b.

\(\left(\frac{2}{11\times13}+\frac{2}{13\times15}+...+\frac{2}{19\times21}\right)-x+\frac{221}{231}=\frac{4}{3}\)

\(\left(\frac{1}{11}-\frac{1}{13}+\frac{1}{13}-\frac{1}{15}+...+\frac{1}{19}-\frac{1}{21}\right)+\frac{221}{231}-x=\frac{4}{3}\)

\(\left(\frac{1}{11}-\frac{1}{21}\right)+\frac{221}{231}-x=\frac{4}{3}\)

\(\left(\frac{21-11}{231}\right)+\frac{221}{231}-x=\frac{4}{3}\)

\(\frac{10}{231}+\frac{221}{231}-x=\frac{4}{3}\)

\(\frac{231}{231}-x=\frac{4}{3}\)

\(1-x=\frac{4}{3}\)

\(x=1-\frac{4}{3}\)

\(x=\frac{3-4}{3}\)

\(x=-\frac{1}{3}\)

Chúc bạn học tốt