Question

Tìm x:

( \(\frac{2}{11x13}+\frac{2}{13x15}+\frac{2}{15x17}+\frac{2}{17x19}+\frac{2}{29x21}\) ) x 462 - x=19

Help me please! Thanks a lot!

Answer 1

\(\left(\frac{2}{11.13}+\frac{2}{13.15}+...+\frac{2}{19.21}\right).462-x=19\)

\(\left(\frac{1}{11}-\frac{1}{13}+...+\frac{1}{19}-\frac{1}{21}\right)\cdot462-x=19\)

\(\left(\frac{1}{11}-\frac{1}{21}\right)\cdot462-x=19\)

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

\(20-x=19\)

\(x=20-19\)

\(x=1\)

Answer 2

Đề abfi sai. Chỗ đó là 19, k phải 29

Bạn biết tính chất này không?

\(\frac{a}{n\left(n+a\right)}=\frac{1}{n}-\frac{1}{n+a}\)

Sử dụng tính chất đó thì được:

\(\left(\frac{2}{11}-\frac{2}{13}+\frac{2}{13}-\frac{2}{15}+...+\frac{2}{19}-\frac{2}{21}\right)\)x 462 - x =19

\(\left(\frac{2}{11}-\frac{2}{21}\right)\cdot462-x=19\)

\(\frac{924}{11}-\frac{924}{21}-x=19\)

84 - 44 - x =19

40 - x = 19

x = 40 - 19

x = 21

Nhớ tk cho mình nếu đúng nhé

Answer 3

\(\left(\frac{2}{11.13}+\frac{2}{13.15}+.....+\frac{2}{19.21}\right).462-x=19\)

\(\Leftrightarrow\left(\frac{1}{11}-\frac{1}{13}+\frac{1}{13}-\frac{1}{15}+......+\frac{1}{19}-\frac{1}{21}\right).462-x=19\)

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

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

\(\Leftrightarrow20-x=19\)

\(\Leftrightarrow x=20-19\)

\(\Leftrightarrow x=1\)

Answer 4

\(\left(\frac{2}{11.13}+\frac{2}{13.15}+.....+\frac{2}{19.21}\right).462-x=19\)

\(\left(\frac{1}{11}-\frac{1}{13}+\frac{1}{13}-\frac{1}{15}+.....+\frac{1}{19}-\frac{1}{21}\right).462-x=19\)

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

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

\(20-x=19\)

\(x=20-19\)

\(x=1\)