Question

[Nguyen phuong oanh]

 [2/11.13+2/13.15+2/15.17+2/17.19+2/19.20].462-x=19

Answer 1

[Nguyên]

Đặt \(A=\frac{2}{11.13}+\frac{2}{13.15}+\frac{2}{15.17}+\frac{2}{17.19}+\frac{2}{19.21}^{ }\)

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

\(A=\frac{1}{11}-\frac{1}{21}\)

\(A=\frac{10}{231}\)

Thay \(A=\frac{10}{231}\) vào ta có

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

\(20-x=19\)

\(x=20-19\)

\(x=1\)

Answer 2

[Nguyên]

boi vi\(\frac{10}{231}.462=20\) cho mik dung nha